HTML

Living Standard — Last Updated 12 December 2024

1. 1. 1. 4.10.5 The input element
         1. 4.10.5.1 States of the type attribute
            1. 4.10.5.1.1 Hidden state (type=hidden)
            2. 4.10.5.1.2 Text (type=text) state and Search state (type=search)
            3. 4.10.5.1.3 Telephone state (type=tel)
            4. 4.10.5.1.4 URL state (type=url)
            5. 4.10.5.1.5 Email state (type=email)
            6. 4.10.5.1.6 Password state (type=password)
            7. 4.10.5.1.7 Date state (type=date)
            8. 4.10.5.1.8 Month state (type=month)
            9. 4.10.5.1.9 Week state (type=week)
            10. 4.10.5.1.10 Time state (type=time)
            11. 4.10.5.1.11 Local Date and Time state (type=datetime-local)
            12. 4.10.5.1.12 Number state (type=number)
            13. 4.10.5.1.13 Range state (type=range)
            14. 4.10.5.1.14 Color state (type=color)
            15. 4.10.5.1.15 Checkbox state (type=checkbox)
            16. 4.10.5.1.16 Radio Button state (type=radio)
            17. 4.10.5.1.17 File Upload state (type=file)
            18. 4.10.5.1.18 Submit Button state (type=submit)
            19. 4.10.5.1.19 Image Button state (type=image)
            20. 4.10.5.1.20 Reset Button state (type=reset)
            21. 4.10.5.1.21 Button state (type=button)
         2. 4.10.5.2 Implementation notes regarding localization of form controls
         3. 4.10.5.3 Common input element attributes
            1. 4.10.5.3.1 The maxlength and minlength attributes
            2. 4.10.5.3.2 The size attribute
            3. 4.10.5.3.3 The readonly attribute
            4. 4.10.5.3.4 The required attribute
            5. 4.10.5.3.5 The multiple attribute
            6. 4.10.5.3.6 The pattern attribute
            7. 4.10.5.3.7 The min and max attributes
            8. 4.10.5.3.8 The step attribute
            9. 4.10.5.3.9 The list attribute
            10. 4.10.5.3.10 The placeholder attribute
         4. 4.10.5.4 Common input element APIs
         5. 4.10.5.5 Common event behaviors

4.10.5 The input element

Categories:

Flow content.

Phrasing content.

If the type attribute is not in the Hidden state: Interactive content.

If the type attribute is not in the Hidden state: Listed, labelable, submittable, resettable, and autocapitalize-and-autocorrect inheriting form-associated element.

If the type attribute is in the Hidden state: Listed, submittable, resettable, and autocapitalize-and-autocorrect inheriting form-associated element.

If the type attribute is not in the Hidden state: Palpable content.

Contexts in which this element can be used:

Where phrasing content is expected.

Content model:

Nothing.

Tag omission in text/html:

No end tag.

Content attributes:

Global attributes

accept — Hint for expected file type in file upload controls

alpha — Allow the color's alpha component to be set

alt — Replacement text for use when images are not available

autocomplete — Hint for form autofill feature

checked — Whether the control is checked

colorspace — The color space of the serialized color

dirname — Name of form control to use for sending the element's directionality in form submission

disabled — Whether the form control is disabled

form — Associates the element with a form element

formaction — URL to use for form submission

formenctype — Entry list encoding type to use for form submission

formmethod — Variant to use for form submission

formnovalidate — Bypass form control validation for form submission

formtarget — Navigable for form submission

height — Vertical dimension

list — List of autocomplete options

max — Maximum value

maxlength — Maximum length of value

min — Minimum value

minlength — Minimum length of value

multiple — Whether to allow multiple values

name — Name of the element to use for form submission and in the form.elements API

pattern — Pattern to be matched by the form control's value

placeholder — User-visible label to be placed within the form control

popovertarget — Targets a popover element to toggle, show, or hide

popovertargetaction — Indicates whether a targeted popover element is to be toggled, shown, or hidden

readonly — Whether to allow the value to be edited by the user

required — Whether the control is required for form submission

size — Size of the control

src — Address of the resource

step — Granularity to be matched by the form control's value

type — Type of form control

value — Value of the form control

width — Horizontal dimension

Also, the title attribute has special semantics on this element: Description of pattern (when used with pattern attribute)

Accessibility considerations:

type attribute in the Hidden state: for authors; for implementers.

type attribute in the Text state: for authors; for implementers.

type attribute in the Search state: for authors; for implementers.

type attribute in the Telephone state: for authors; for implementers.

type attribute in the URL state: for authors; for implementers.

type attribute in the Email state: for authors; for implementers.

type attribute in the Password state: for authors; for implementers.

type attribute in the Date state: for authors; for implementers.

type attribute in the Month state: for authors; for implementers.

type attribute in the Week state: for authors; for implementers.

type attribute in the Time state: for authors; for implementers.

type attribute in the Local Date and Time state: for authors; for implementers.

type attribute in the Number state: for authors; for implementers.

type attribute in the Range state: for authors; for implementers.

type attribute in the Color state: for authors; for implementers.

type attribute in the Checkbox state: for authors; for implementers.

type attribute in the Radio Button state: for authors; for implementers.

type attribute in the File Upload state: for authors; for implementers.

type attribute in the Submit Button state: for authors; for implementers.

type attribute in the Image Button state: for authors; for implementers.

type attribute in the Reset Button state: for authors; for implementers.

type attribute in the Button state: for authors; for implementers.

DOM interface:

[Exposed=Window]
interface HTMLInputElement : HTMLElement {
  [HTMLConstructor] constructor();

  [CEReactions] attribute DOMString accept;
  [CEReactions] attribute boolean alpha;
  [CEReactions] attribute DOMString alt;
  [CEReactions] attribute DOMString autocomplete;
  [CEReactions] attribute boolean defaultChecked;
  attribute boolean checked;
  [CEReactions] attribute DOMString colorSpace;
  [CEReactions] attribute DOMString dirName;
  [CEReactions] attribute boolean disabled;
  readonly attribute HTMLFormElement? form;
  attribute FileList? files;
  [CEReactions] attribute USVString formAction;
  [CEReactions] attribute DOMString formEnctype;
  [CEReactions] attribute DOMString formMethod;
  [CEReactions] attribute boolean formNoValidate;
  [CEReactions] attribute DOMString formTarget;
  [CEReactions] attribute unsigned long height;
  attribute boolean indeterminate;
  readonly attribute HTMLDataListElement? list;
  [CEReactions] attribute DOMString max;
  [CEReactions] attribute long maxLength;
  [CEReactions] attribute DOMString min;
  [CEReactions] attribute long minLength;
  [CEReactions] attribute boolean multiple;
  [CEReactions] attribute DOMString name;
  [CEReactions] attribute DOMString pattern;
  [CEReactions] attribute DOMString placeholder;
  [CEReactions] attribute boolean readOnly;
  [CEReactions] attribute boolean required;
  [CEReactions] attribute unsigned long size;
  [CEReactions] attribute USVString src;
  [CEReactions] attribute DOMString step;
  [CEReactions] attribute DOMString type;
  [CEReactions] attribute DOMString defaultValue;
  [CEReactions] attribute [LegacyNullToEmptyString] DOMString value;
  attribute object? valueAsDate;
  attribute unrestricted double valueAsNumber;
  [CEReactions] attribute unsigned long width;

  undefined stepUp(optional long n = 1);
  undefined stepDown(optional long n = 1);

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  boolean reportValidity();
  undefined setCustomValidity(DOMString error);

  readonly attribute NodeList? labels;

  undefined select();
  attribute unsigned long? selectionStart;
  attribute unsigned long? selectionEnd;
  attribute DOMString? selectionDirection;
  undefined setRangeText(DOMString replacement);
  undefined setRangeText(DOMString replacement, unsigned long start, unsigned long end, optional SelectionMode selectionMode = "preserve");
  undefined setSelectionRange(unsigned long start, unsigned long end, optional DOMString direction);

  undefined showPicker();

  // also has obsolete members
};
HTMLInputElement includes PopoverInvokerElement;

The input element represents a typed data field, usually with a form control to allow the user to edit the data.

The type attribute controls the data type (and associated control) of the element. It is an enumerated attribute with the following keywords and states:

The attribute's missing value default and invalid value default are both the Text state.

Which of the accept, alpha, alt, autocomplete, checked, colorspace, dirname, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, minlength, multiple, pattern, placeholder, readonly, required, size, src, step, and width content attributes, the checked, files, valueAsDate, valueAsNumber, and list IDL attributes, the select() method, the selectionStart, selectionEnd, and selectionDirection, IDL attributes, the setRangeText() and setSelectionRange() methods, the stepUp() and stepDown() methods, and the input and change events apply to an input element depends on the state of its type attribute. The subsections that define each type also clearly define in normative "bookkeeping" sections which of these feature apply, and which do not apply, to each type. The behavior of these features depends on whether they apply or not, as defined in their various sections (q.v. for content attributes, for APIs, for events).

The following table is non-normative and summarizes which of those content attributes, IDL attributes, methods, and events apply to each state:

† If the control has no selectable text, the select() method results in a no-op, with no "InvalidStateError" DOMException.

Some states of the type attribute define a value sanitization algorithm.

Each input element has a value, which is exposed by the value IDL attribute. Some states define an algorithm to convert a string to a number, an algorithm to convert a number to a string, an algorithm to convert a string to a Date object, and an algorithm to convert a Date object to a string, which are used by max, min, step, valueAsDate, valueAsNumber, and stepUp().

An input element's dirty value flag must be set to true whenever the user interacts with the control in a way that changes the value. (It is also set to true when the value is programmatically changed, as described in the definition of the value IDL attribute.)

The value content attribute gives the default value of the input element. When the value content attribute is added, set, or removed, if the control's dirty value flag is false, the user agent must set the value of the element to the value of the value content attribute, if there is one, or the empty string otherwise, and then run the current value sanitization algorithm, if one is defined.

Each input element has a checkedness, which is exposed by the checked IDL attribute.

Each input element has a boolean dirty checkedness flag. When it is true, the element is said to have a dirty checkedness. The dirty checkedness flag must be initially set to false when the element is created, and must be set to true whenever the user interacts with the control in a way that changes the checkedness.

The checked content attribute is a boolean attribute that gives the default checkedness of the input element. When the checked content attribute is added, if the control does not have dirty checkedness, the user agent must set the checkedness of the element to true; when the checked content attribute is removed, if the control does not have dirty checkedness, the user agent must set the checkedness of the element to false.

The reset algorithm for input elements is to set its user validity, dirty value flag, and dirty checkedness flag back to false, set the value of the element to the value of the value content attribute, if there is one, or the empty string otherwise, set the checkedness of the element to true if the element has a checked content attribute and false if it does not, empty the list of selected files, and then invoke the value sanitization algorithm, if the type attribute's current state defines one.

Each input element can be mutable. Except where otherwise specified, an input element is always mutable. Similarly, except where otherwise specified, the user agent should not allow the user to modify the element's value or checkedness.

When an input element is disabled, it is not mutable.

The readonly attribute can also in some cases (e.g. for the Date state, but not the Checkbox state) stop an input element from being mutable.

The input element can support a picker. A picker is a user interface element that allows the end user to choose a value. Whether an input element supports a picker depends on the type attribute state and implementation-defined behavior. An input element must support a picker when its type attribute is in the File Upload state.

The cloning steps for input elements must propagate the value, dirty value flag, checkedness, and dirty checkedness flag from the node being cloned to the copy.

The activation behavior for input elements element, given event, are these steps:

1. If element is not mutable and is not in the Checkbox state and is not in the Radio state, then return.

2. Run element's input activation behavior, if any, and do nothing otherwise.

3. Run the popover target attribute activation behavior given element and event's target.

Recall that an element's activation behavior runs for both user-initiated activations and for synthetic activations (e.g., via el.click()). User agents might also have behaviors for a given control — not specified here — that are triggered only by true user-initiated activations. A common choice is to show the picker, if applicable, for the control. In contrast, the input activation behavior only shows pickers for the special historical cases of the File Upload and Color states.

The legacy-pre-activation behavior for input elements are these steps:

1. If this element's type attribute is in the Checkbox state, then set this element's checkedness to its opposite value (i.e. true if it is false, false if it is true) and set this element's indeterminate IDL attribute to false.

2. If this element's type attribute is in the Radio Button state, then get a reference to the element in this element's radio button group that has its checkedness set to true, if any, and then set this element's checkedness to true.

The legacy-canceled-activation behavior for input elements are these steps:

1. If the element's type attribute is in the Checkbox state, then set the element's checkedness and the element's indeterminate IDL attribute back to the values they had before the legacy-pre-activation behavior was run.

2. If this element's type attribute is in the Radio Button state, then if the element to which a reference was obtained in the legacy-pre-activation behavior, if any, is still in what is now this element's radio button group, if it still has one, and if so, setting that element's checkedness to true; or else, if there was no such element, or that element is no longer in this element's radio button group, or if this element no longer has a radio button group, setting this element's checkedness to false.

When an input element is first created, the element's rendering and behavior must be set to the rendering and behavior defined for the type attribute's state, and the value sanitization algorithm, if one is defined for the type attribute's state, must be invoked.

The name attribute represents the element's name. The dirname attribute controls how the element's directionality is submitted. The disabled attribute is used to make the control non-interactive and to prevent its value from being submitted. The form attribute is used to explicitly associate the input element with its form owner. The autocomplete attribute controls how the user agent provides autofill behavior.

The indeterminate IDL attribute must initially be set to false. On getting, it must return the last value it was set to. On setting, it must be set to the new value. It has no effect except for changing the appearance of checkbox controls.

The accept, alpha, alt, max, min, multiple, pattern, placeholder, required, size, src, and step IDL attributes must reflect the respective content attributes of the same name. The dirName IDL attribute must reflect the dirname content attribute. The readOnly IDL attribute must reflect the readonly content attribute. The defaultChecked IDL attribute must reflect the checked content attribute. The defaultValue IDL attribute must reflect the value content attribute.

The colorSpace IDL attribute must reflect the colorspace content attribute, limited to only known values. The type IDL attribute must reflect the respective content attribute of the same name, limited to only known values. The maxLength IDL attribute must reflect the maxlength content attribute, limited to only non-negative numbers. The minLength IDL attribute must reflect the minlength content attribute, limited to only non-negative numbers.

The IDL attributes width and height must return the rendered width and height of the image, in CSS pixels, if an image is being rendered; or else the natural width and height of the image, in CSS pixels, if an image is available but not being rendered; or else 0, if no image is available. When the input element's type attribute is not in the Image Button state, then no image is available. [CSS]

On setting, they must act as if they reflected the respective content attributes of the same name.

The willValidate, validity, and validationMessage IDL attributes, and the checkValidity(), reportValidity(), and setCustomValidity() methods, are part of the constraint validation API. The labels IDL attribute provides a list of the element's labels. The select(), selectionStart, selectionEnd, selectionDirection, setRangeText(), and setSelectionRange() methods and IDL attributes expose the element's text selection. The disabled, form, and name IDL attributes are part of the element's forms API.

4.10.5.1 States of the type attribute

4.10.5.1.1 Hidden state (type=hidden)

When an input element's type attribute is in the Hidden state, the rules in this section apply.

The input element represents a value that is not intended to be examined or manipulated by the user.

Constraint validation: If an input element's type attribute is in the Hidden state, it is barred from constraint validation.

If the name attribute is present and has a value that is an ASCII case-insensitive match for "_charset_", then the element's value attribute must be omitted.

4.10.5.1.2 Text (type=text) state and Search state (type=search)

When an input element's type attribute is in the Text state or the Search state, the rules in this section apply.

The input element represents a one line plain text edit control for the element's value.

The difference between the Text state and the Search state is primarily stylistic: on platforms where search controls are distinguished from regular text controls, the Search state might result in an appearance consistent with the platform's search controls rather than appearing like a regular text control.

If the element is mutable, its value should be editable by the user. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the element's value.

If the element is mutable, the user agent should allow the user to change the writing direction of the element, setting it either to a left-to-right writing direction or a right-to-left writing direction. If the user does so, the user agent must then run the following steps:

1. Set the element's dir attribute to "ltr" if the user selected a left-to-right writing direction, and "rtl" if the user selected a right-to-left writing direction.

2. Queue an element task on the user interaction task source given the element to fire an event named input at the element, with the bubbles and composed attributes initialized to true.

The value attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

The value sanitization algorithm is as follows: Strip newlines from the value.

4.10.5.1.3 Telephone state (type=tel)

When an input element's type attribute is in the Telephone state, the rules in this section apply.

The input element represents a control for editing a telephone number given in the element's value.

If the element is mutable, its value should be editable by the user. User agents may change the spacing and, with care, the punctuation of values that the user enters. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the element's value.

The value attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

The value sanitization algorithm is as follows: Strip newlines from the value.

Unlike the URL and Email types, the Telephone type does not enforce a particular syntax. This is intentional; in practice, telephone number fields tend to be free-form fields, because there are a wide variety of valid phone numbers. Systems that need to enforce a particular format are encouraged to use the pattern attribute or the setCustomValidity() method to hook into the client-side validation mechanism.

4.10.5.1.4 URL state (type=url)

When an input element's type attribute is in the URL state, the rules in this section apply.

The input element represents a control for editing a single absolute URL given in the element's value.

If the element is mutable, the user agent should allow the user to change the URL represented by its value. User agents may allow the user to set the value to a string that is not a valid absolute URL, but may also or instead automatically escape characters entered by the user so that the value is always a valid absolute URL (even if that isn't the actual value seen and edited by the user in the interface). User agents should allow the user to set the value to the empty string. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the value.

The value attribute, if specified and not empty, must have a value that is a valid URL potentially surrounded by spaces that is also an absolute URL.

The value sanitization algorithm is as follows: Strip newlines from the value, then strip leading and trailing ASCII whitespace from the value.

Constraint validation: While the value of the element is neither the empty string nor a valid absolute URL, the element is suffering from a type mismatch.

<input type="url" name="location" list="urls">
<datalist id="urls">
 <option label="MIME: Format of Internet Message Bodies" value="https://www.rfc-editor.org/rfc/rfc2045">
 <option label="HTML" value="https://html.spec.whatwg.org/">
 <option label="DOM" value="https://dom.spec.whatwg.org/">
 <option label="Fullscreen" value="https://fullscreen.spec.whatwg.org/">
 <option label="Media Session" value="https://mediasession.spec.whatwg.org/">
 <option label="The Single UNIX Specification, Version 3" value="http://www.unix.org/version3/">
</datalist>

4.10.5.1.5 Email state (type=email)

When an input element's type attribute is in the Email state, the rules in this section apply.

How the Email state operates depends on whether the multiple attribute is specified or not.

When the multiple attribute is not specified on the element

The input element represents a control for editing an email address given in the element's value.

If the element is mutable, the user agent should allow the user to change the email address represented by its value. User agents may allow the user to set the value to a string that is not a valid email address. The user agent should act in a manner consistent with expecting the user to provide a single email address. User agents should allow the user to set the value to the empty string. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the value. User agents may transform the value for display and editing; in particular, user agents should convert punycode in the domain labels of the value to IDN in the display and vice versa.

Constraint validation: While the user interface is representing input that the user agent cannot convert to punycode, the control is suffering from bad input.

The value attribute, if specified and not empty, must have a value that is a single valid email address.

The value sanitization algorithm is as follows: Strip newlines from the value, then strip leading and trailing ASCII whitespace from the value.

Constraint validation: While the value of the element is neither the empty string nor a single valid email address, the element is suffering from a type mismatch.

When the multiple attribute is specified on the element

The input element represents a control for adding, removing, and editing the email addresses given in the element's values.

If the element is mutable, the user agent should allow the user to add, remove, and edit the email addresses represented by its values. User agents may allow the user to set any individual value in the list of values to a string that is not a valid email address, but must not allow users to set any individual value to a string containing U+002C COMMA (,), U+000A LINE FEED (LF), or U+000D CARRIAGE RETURN (CR) characters. User agents should allow the user to remove all the addresses in the element's values. User agents may transform the values for display and editing; in particular, user agents should convert punycode in the domain labels of the value to IDN in the display and vice versa.

Constraint validation: While the user interface describes a situation where an individual value contains a U+002C COMMA (,) or is representing input that the user agent cannot convert to punycode, the control is suffering from bad input.

Whenever the user changes the element's values, the user agent must run the following steps:

1. Let latest values be a copy of the element's values.

2. Strip leading and trailing ASCII whitespace from each value in latest values.

3. Let the element's value be the result of concatenating all the values in latest values, separating each value from the next by a single U+002C COMMA character (,), maintaining the list's order.

The value attribute, if specified, must have a value that is a valid email address list.

The value sanitization algorithm is as follows:

1. Split on commas the element's value, strip leading and trailing ASCII whitespace from each resulting token, if any, and let the element's values be the (possibly empty) resulting list of (possibly empty) tokens, maintaining the original order.

2. Let the element's value be the result of concatenating the element's values, separating each value from the next by a single U+002C COMMA character (,), maintaining the list's order.

Constraint validation: While the value of the element is not a valid email address list, the element is suffering from a type mismatch.

When the multiple attribute is set or removed, the user agent must run the value sanitization algorithm.

A valid email address is a string that matches the email production of the following ABNF, the character set for which is Unicode. This ABNF implements the extensions described in RFC 1123. [ABNF] [RFC5322] [RFC1034] [RFC1123]

email         = 1*( atext / "." ) "@" label *( "." label )
label         = let-dig [ [ ldh-str ] let-dig ]  ; limited to a length of 63 characters by RFC 1034 section 3.5
atext         = < as defined in RFC 5322 section 3.2.3 >
let-dig       = < as defined in RFC 1034 section 3.5 >
ldh-str       = < as defined in RFC 1034 section 3.5 >

This requirement is a willful violation of RFC 5322, which defines a syntax for email addresses that is simultaneously too strict (before the "@" character), too vague (after the "@" character), and too lax (allowing comments, whitespace characters, and quoted strings in manners unfamiliar to most users) to be of practical use here.

/^[a-zA-Z0-9.!#$%&'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/

A valid email address list is a set of comma-separated tokens, where each token is itself a valid email address. To obtain the list of tokens from a valid email address list, an implementation must split the string on commas.

4.10.5.1.6 Password state (type=password)

When an input element's type attribute is in the Password state, the rules in this section apply.

The input element represents a one line plain text edit control for the element's value. The user agent should obscure the value so that people other than the user cannot see it.

If the element is mutable, its value should be editable by the user. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the value.

The value attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

The value sanitization algorithm is as follows: Strip newlines from the value.

4.10.5.1.7 Date state (type=date)

When an input element's type attribute is in the Date state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific date.

If the element is mutable, the user agent should allow the user to change the date represented by its value, as obtained by parsing a date from it. User agents must not allow the user to set the value to a non-empty string that is not a valid date string. If the user agent provides a user interface for selecting a date, then the value must be set to a valid date string representing the user's selection. User agents should allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid date string, the control is suffering from bad input.

See the introduction section for a discussion of the difference between the input format and submission format for date, time, and number form controls, and the implementation notes regarding localization of form controls.

The value attribute, if specified and not empty, must have a value that is a valid date string.

The value sanitization algorithm is as follows: If the value of the element is not a valid date string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid date string. The max attribute, if specified, must have a value that is a valid date string.

The step attribute is expressed in days. The step scale factor is 86,400,000 (which converts the days to milliseconds, as used in the other algorithms). The default step is 1 day.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest date for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a date from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z") to midnight UTC on the morning of the parsed date, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid date string that represents the date that, in UTC, is current input milliseconds after midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z").

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a date from input results in an error, then return an error; otherwise, return a new Date object representing midnight UTC on the morning of the parsed date.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid date string that represents the date current at the time represented by input in the UTC time zone.

4.10.5.1.8 Month state (type=month)

When an input element's type attribute is in the Month state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific month.

If the element is mutable, the user agent should allow the user to change the month represented by its value, as obtained by parsing a month from it. User agents must not allow the user to set the value to a non-empty string that is not a valid month string. If the user agent provides a user interface for selecting a month, then the value must be set to a valid month string representing the user's selection. User agents should allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid month string, the control is suffering from bad input.

See the introduction section for a discussion of the difference between the input format and submission format for date, time, and number form controls, and the implementation notes regarding localization of form controls.

The value attribute, if specified and not empty, must have a value that is a valid month string.

The value sanitization algorithm is as follows: If the value of the element is not a valid month string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid month string. The max attribute, if specified, must have a value that is a valid month string.

The step attribute is expressed in months. The step scale factor is 1 (there is no conversion needed as the algorithms use months). The default step is 1 month.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest month for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a month from input results in an error, then return an error; otherwise, return the number of months between January 1970 and the parsed month.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid month string that represents the month that has input months between it and January 1970.

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a month from input results in an error, then return an error; otherwise, return a new Date object representing midnight UTC on the morning of the first day of the parsed month.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid month string that represents the month current at the time represented by input in the UTC time zone.

4.10.5.1.9 Week state (type=week)

When an input element's type attribute is in the Week state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific week.

If the element is mutable, the user agent should allow the user to change the week represented by its value, as obtained by parsing a week from it. User agents must not allow the user to set the value to a non-empty string that is not a valid week string. If the user agent provides a user interface for selecting a week, then the value must be set to a valid week string representing the user's selection. User agents should allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid week string, the control is suffering from bad input.

See the introduction section for a discussion of the difference between the input format and submission format for date, time, and number form controls, and the implementation notes regarding localization of form controls.

The value attribute, if specified and not empty, must have a value that is a valid week string.

The value sanitization algorithm is as follows: If the value of the element is not a valid week string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid week string. The max attribute, if specified, must have a value that is a valid week string.

The step attribute is expressed in weeks. The step scale factor is 604,800,000 (which converts the weeks to milliseconds, as used in the other algorithms). The default step is 1 week. The default step base is −259,200,000 (the start of week 1970-W01).

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest week for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a week string from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z") to midnight UTC on the morning of the Monday of the parsed week, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid week string that represents the week that, in UTC, is current input milliseconds after midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z").

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a week from input results in an error, then return an error; otherwise, return a new Date object representing midnight UTC on the morning of the Monday of the parsed week.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid week string that represents the week current at the time represented by input in the UTC time zone.

4.10.5.1.10 Time state (type=time)

When an input element's type attribute is in the Time state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific time.

If the element is mutable, the user agent should allow the user to change the time represented by its value, as obtained by parsing a time from it. User agents must not allow the user to set the value to a non-empty string that is not a valid time string. If the user agent provides a user interface for selecting a time, then the value must be set to a valid time string representing the user's selection. User agents should allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid time string, the control is suffering from bad input.

See the introduction section for a discussion of the difference between the input format and submission format for date, time, and number form controls, and the implementation notes regarding localization of form controls.

The value attribute, if specified and not empty, must have a value that is a valid time string.

The value sanitization algorithm is as follows: If the value of the element is not a valid time string, then set it to the empty string instead.

The form control has a periodic domain.

The min attribute, if specified, must have a value that is a valid time string. The max attribute, if specified, must have a value that is a valid time string.

The step attribute is expressed in seconds. The step scale factor is 1000 (which converts the seconds to milliseconds, as used in the other algorithms). The default step is 60 seconds.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest time for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a time from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight to the parsed time on a day with no time changes.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid time string that represents the time that is input milliseconds after midnight on a day with no time changes.

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a time from input results in an error, then return an error; otherwise, return a new Date object representing the parsed time in UTC on 1970-01-01.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid time string that represents the UTC time component that is represented by input.

4.10.5.1.11 Local Date and Time state (type=datetime-local)

When an input element's type attribute is in the Local Date and Time state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a local date and time, with no time-zone offset information.

If the element is mutable, the user agent should allow the user to change the date and time represented by its value, as obtained by parsing a date and time from it. User agents must not allow the user to set the value to a non-empty string that is not a valid normalized local date and time string. If the user agent provides a user interface for selecting a local date and time, then the value must be set to a valid normalized local date and time string representing the user's selection. User agents should allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid normalized local date and time string, the control is suffering from bad input.

See the introduction section for a discussion of the difference between the input format and submission format for date, time, and number form controls, and the implementation notes regarding localization of form controls.

The value attribute, if specified and not empty, must have a value that is a valid local date and time string.

The value sanitization algorithm is as follows: If the value of the element is a valid local date and time string, then set it to a valid normalized local date and time string representing the same date and time; otherwise, set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid local date and time string. The max attribute, if specified, must have a value that is a valid local date and time string.

The step attribute is expressed in seconds. The step scale factor is 1000 (which converts the seconds to milliseconds, as used in the other algorithms). The default step is 60 seconds.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest local date and time for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a date and time from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0") to the parsed local date and time, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid normalized local date and time string that represents the date and time that is input milliseconds after midnight on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0").

See the note on historical dates in the Date state section.

<fieldset>
 <legend>Destination</legend>
 <p><label>Airport: <input type=text name=to list=airports></label></p>
 <p><label>Departure time: <input type=datetime-local name=totime step=3600></label></p>
</fieldset>
<datalist id=airports>
 <option value=ATL label="Atlanta">
 <option value=MEM label="Memphis">
 <option value=LHR label="London Heathrow">
 <option value=LAX label="Los Angeles">
 <option value=FRA label="Frankfurt">
</datalist>

4.10.5.1.12 Number state (type=number)

When an input element's type attribute is in the Number state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a number.

If the element is mutable, the user agent should allow the user to change the number represented by its value, as obtained from applying the rules for parsing floating-point number values to it. User agents must not allow the user to set the value to a non-empty string that is not a valid floating-point number. If the user agent provides a user interface for selecting a number, then the value must be set to the best representation of the number representing the user's selection as a floating-point number. User agents should allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid floating-point number, the control is suffering from bad input.

This specification does not define what user interface user agents are to use; user agent vendors are encouraged to consider what would best serve their users' needs. For example, a user agent in Persian or Arabic markets might support Persian and Arabic numeric input (converting it to the format required for submission as described above). Similarly, a user agent designed for Romans might display the value in Roman numerals rather than in decimal; or (more realistically) a user agent designed for the French market might display the value with apostrophes between thousands and commas before the decimals, and allow the user to enter a value in that manner, internally converting it to the submission format described above.

The value attribute, if specified and not empty, must have a value that is a valid floating-point number.

The value sanitization algorithm is as follows: If the value of the element is not a valid floating-point number, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid floating-point number. The max attribute, if specified, must have a value that is a valid floating-point number.

The step scale factor is 1. The default step is 1 (allowing only integers to be selected by the user, unless the step base has a non-integer value).

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest number for which the element would not suffer from a step mismatch. If there are two such numbers, user agents are encouraged to pick the one nearest positive infinity.

The algorithm to convert a string to a number, given a string input, is as follows: If applying the rules for parsing floating-point number values to input results in an error, then return an error; otherwise, return the resulting number.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid floating-point number that represents input.

<label>How much do you want to charge? $<input type=number min=0 step=0.01 name=price></label>

The type=number state is not appropriate for input that happens to only consist of numbers but isn't strictly speaking a number. For example, it would be inappropriate for credit card numbers or US postal codes. A simple way of determining whether to use type=number is to consider whether it would make sense for the input control to have a spinbox interface (e.g. with "up" and "down" arrows). Getting a credit card number wrong by 1 in the last digit isn't a minor mistake, it's as wrong as getting every digit incorrect. So it would not make sense for the user to select a credit card number using "up" and "down" buttons. When a spinbox interface is not appropriate, type=text is probably the right choice (possibly with an inputmode or pattern attribute).

4.10.5.1.13 Range state (type=range)

When an input element's type attribute is in the Range state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a number, but with the caveat that the exact value is not important, letting UAs provide a simpler interface than they do for the Number state.

If the element is mutable, the user agent should allow the user to change the number represented by its value, as obtained from applying the rules for parsing floating-point number values to it. User agents must not allow the user to set the value to a string that is not a valid floating-point number. If the user agent provides a user interface for selecting a number, then the value must be set to a best representation of the number representing the user's selection as a floating-point number. User agents must not allow the user to set the value to the empty string.

Constraint validation: While the user interface describes input that the user agent cannot convert to a valid floating-point number, the control is suffering from bad input.

The value attribute, if specified, must have a value that is a valid floating-point number.

The value sanitization algorithm is as follows: If the value of the element is not a valid floating-point number, then set it to the best representation, as a floating-point number, of the default value.

The default value is the minimum plus half the difference between the minimum and the maximum, unless the maximum is less than the minimum, in which case the default value is the minimum.

When the element is suffering from an underflow, the user agent must set the element's value to the best representation, as a floating-point number, of the minimum.

When the element is suffering from an overflow, if the maximum is not less than the minimum, the user agent must set the element's value to a valid floating-point number that represents the maximum.

When the element is suffering from a step mismatch, the user agent must round the element's value to the nearest number for which the element would not suffer from a step mismatch, and which is greater than or equal to the minimum, and, if the maximum is not less than the minimum, which is less than or equal to the maximum, if there is a number that matches these constraints. If two numbers match these constraints, then user agents must use the one nearest to positive infinity.

For example, the markup <input type="range" min=0 max=100 step=20 value=50> results in a range control whose initial value is 60.

<input type="range" min="-100" max="100" value="0" step="10" name="power" list="powers">
<datalist id="powers">
<option value="0">
<option value="-30">
<option value="30">
 <option value="++50">
</datalist>

input { writing-mode: vertical-lr; height: 75px; width: 49px; background: #D5CCBB; color: black; }

<input name=x type=range min=100 max=700 step=9.09090909 value=509.090909>

<input type="range" name="a" list="a-values">
<datalist id="a-values">
<option value="10" label="Low">
<option value="90" label="High">
</datalist>

In this state, the range and step constraints are enforced even during user input, and there is no way to set the value to the empty string.

The min attribute, if specified, must have a value that is a valid floating-point number. The default minimum is 0. The max attribute, if specified, must have a value that is a valid floating-point number. The default maximum is 100.

The step scale factor is 1. The default step is 1 (allowing only integers, unless the min attribute has a non-integer value).

The algorithm to convert a string to a number, given a string input, is as follows: If applying the rules for parsing floating-point number values to input results in an error, then return an error; otherwise, return the resulting number.

The algorithm to convert a number to a string, given a number input, is as follows: Return the best representation, as a floating-point number, of input.

4.10.5.1.14 Color state (type=color)

When an input element's type attribute is in the Color state, the rules in this section apply.

The input element represents a color well control, for setting the element's value to a string representing the serialization of a CSS color.

In this state, there is always a CSS color picked, and there is no way for the end user to set the value to the empty string.

The alpha attribute is a boolean attribute. If present, it indicates the CSS color's alpha component can be manipulated by the end user and does not have to be fully opaque.

The colorspace attribute indicates the color space of the serialized CSS color. It also hints at the desired user interface for selecting a CSS color. It is an enumerated attribute with the following keywords and states:

The attribute's missing value default and invalid value default are both the Limited sRGB state.

Whenever the element's alpha or colorspace attributes are changed, the user agent must run update a color well control color given the element.

If the element is mutable, the user agent should allow the user to change the color represented by its value, as obtained from parsing it. User agents must not allow the user to set the value to a string that running update a color well control color for the element would not set it to. If the user agent provides a user interface for selecting a CSS color, then the value must be set to the result of serializing a color well control color given the element and the end user's selection.

The input activation behavior for such an element element is to show the picker, if applicable, for element.

Constraint validation: While the element's value is not the empty string and parsing it returns failure, the control is suffering from bad input.

The value attribute, if specified and not the empty string, must have a value that is a CSS color.

The value sanitization algorithm is as follows: Run update a color well control color for the element.

To update a color well control color, given an element element:

1. Assert: element is an input element whose type attribute is in the Color state.

2. Let color be the result of parsing element's value.

3. If color is failure, then set color to opaque black.

4. Set element's value to the result of serializing a color well control color given element and color.

To serialize a color well control color, given an element element and a CSS color color:

1. Assert: element is an input element whose type attribute is in the Color state.

2. Let htmlCompatible be false.

3. If element's alpha attribute is not specified, then set color's alpha component to be fully opaque.

4. If element's colorspace attribute is in the Limited sRGB state:

   1. Set color to color converted to the 'srgb' color space.

   2. Round each of color's components so they are in the range 0 to 255, inclusive. Components are to be rounded towards +∞.

   3. If element's alpha attribute is not specified, then set htmlCompatible to true.

      This intentionally uses a different serialization path for compatibility with an earlier version of the color well control.

   4. Otherwise, set color to color converted to using the 'color()' function.

5. Otherwise:

   1. Assert: element's colorspace attribute is in the Display P3 state.

   2. Set color to color converted to the 'display-p3' color space.

6. Return the result of serializing color. If htmlCompatible is true, then do so with HTML-compatible serialization requested.

4.10.5.1.15 Checkbox state (type=checkbox)

When an input element's type attribute is in the Checkbox state, the rules in this section apply.

The input element represents a two-state control that represents the element's checkedness state. If the element's checkedness state is true, the control represents a positive selection, and if it is false, a negative selection. If the element's indeterminate IDL attribute is set to true, then the control's selection should be obscured as if the control was in a third, indeterminate, state.

The control is never a true tri-state control, even if the element's indeterminate IDL attribute is set to true. The indeterminate IDL attribute only gives the appearance of a third state.

The input activation behavior is to run the following steps:

1. If the element is not connected, then return.

2. Fire an event named input at the element with the bubbles and composed attributes initialized to true.

3. Fire an event named change at the element with the bubbles attribute initialized to true.

Constraint validation: If the element is required and its checkedness is false, then the element is suffering from being missing.

input.indeterminate [ = value ]

When set, overrides the rendering of checkbox controls so that the current value is not visible.

4.10.5.1.16 Radio Button state (type=radio)

When an input element's type attribute is in the Radio Button state, the rules in this section apply.

The input element represents a control that, when used in conjunction with other input elements, forms a radio button group in which only one control can have its checkedness state set to true. If the element's checkedness state is true, the control represents the selected control in the group, and if it is false, it indicates a control in the group that is not selected.

The radio button group that contains an input element a also contains all the other input elements b that fulfill all of the following conditions:

• The input element b's type attribute is in the Radio Button state.
• Either a and b have the same form owner, or they both have no form owner.
• Both a and b are in the same tree.
• They both have a name attribute, their name attributes are not empty, and the value of a's name attribute equals the value of b's name attribute.

A tree must not contain an input element whose radio button group contains only that element.

When any of the following phenomena occur, if the element's checkedness state is true after the occurrence, the checkedness state of all the other elements in the same radio button group must be set to false:

• The element's checkedness state is set to true (for whatever reason).
• The element's name attribute is set, changed, or removed.
• The element's form owner changes.
• A type change is signalled for the element.

The input activation behavior is to run the following steps:

1. If the element is not connected, then return.

2. Fire an event named input at the element with the bubbles and composed attributes initialized to true.

3. Fire an event named change at the element with the bubbles attribute initialized to true.

Constraint validation: If an element in the radio button group is required, and all of the input elements in the radio button group have a checkedness that is false, then the element is suffering from being missing.

<form>
 <p><label><input type="radio" name="dog-type" value="pupper" required disabled> Pupper</label>
 <p><label><input type="radio" name="dog-type" value="doggo"> Doggo</label>
 <p><button>Make your choice</button>
</form>

If none of the radio buttons in a radio button group are checked, then they will all be initially unchecked in the interface, until such time as one of them is checked (either by the user or by script).

4.10.5.1.17 File Upload state (type=file)

When an input element's type attribute is in the File Upload state, the rules in this section apply.

The input element represents a list of selected files, each file consisting of a filename, a file type, and a file body (the contents of the file).

Filenames must not contain path components, even in the case that a user has selected an entire directory hierarchy or multiple files with the same name from different directories. Path components, for the purposes of the File Upload state, are those parts of filenames that are separated by U+005C REVERSE SOLIDUS character (\) characters.

Unless the multiple attribute is set, there must be no more than one file in the list of selected files.

The input activation behavior for such an element element is to show the picker, if applicable, for element.

If the element is mutable, the user agent should allow the user to change the files on the list in other ways also, e.g., adding or removing files by drag-and-drop. When the user does so, the user agent must update the file selection for the element.

If the element is not mutable, the user agent must not allow the user to change the element's selection.

To update the file selection for an element element:

1. Queue an element task on the user interaction task source given element and the following steps:

   1. Update element's selected files so that it represents the user's selection.

   2. Fire an event named input at the input element, with the bubbles and composed attributes initialized to true.

   3. Fire an event named change at the input element, with the bubbles attribute initialized to true.

Constraint validation: If the element is required and the list of selected files is empty, then the element is suffering from being missing.

The accept attribute may be specified to provide user agents with a hint of what file types will be accepted.

If specified, the attribute must consist of a set of comma-separated tokens, each of which must be an ASCII case-insensitive match for one of the following:

The string "audio/*"

Indicates that sound files are accepted.

The string "video/*"

Indicates that video files are accepted.

The string "image/*"

Indicates that image files are accepted.

A valid MIME type string with no parameters

Indicates that files of the specified type are accepted.

A string whose first character is a U+002E FULL STOP character (.)

Indicates that files with the specified file extension are accepted.

The tokens must not be ASCII case-insensitive matches for any of the other tokens (i.e. duplicates are not allowed). To obtain the list of tokens from the attribute, the user agent must split the attribute value on commas.

User agents may use the value of this attribute to display a more appropriate user interface than a generic file picker. For instance, given the value image/*, a user agent could offer the user the option of using a local camera or selecting a photograph from their photo collection; given the value audio/*, a user agent could offer the user the option of recording a clip using a headset microphone.

User agents should prevent the user from selecting files that are not accepted by one (or more) of these tokens.

Authors are encouraged to specify both any MIME types and any corresponding extensions when looking for data in a specific format.

<input type="file" accept=".doc,.docx,.xml,application/msword,application/vnd.openxmlformats-officedocument.wordprocessingml.document">

Extensions tend to be ambiguous (e.g. there are an untold number of formats that use the ".dat" extension, and users can typically quite easily rename their files to have a ".doc" extension even if they are not Microsoft Word documents), and MIME types tend to be unreliable (e.g. many formats have no formally registered types, and many formats are in practice labeled using a number of different MIME types). Authors are reminded that, as usual, data received from a client should be treated with caution, as it may not be in an expected format even if the user is not hostile and the user agent fully obeyed the accept attribute's requirements.

function extractFilename(path) {
  if (path.substr(0, 12) == "C:\\fakepath\\")
    return path.substr(12); // modern browser
  var x;
  x = path.lastIndexOf('/');
  if (x >= 0) // Unix-based path
    return path.substr(x+1);
  x = path.lastIndexOf('\\');
  if (x >= 0) // Windows-based path
    return path.substr(x+1);
  return path; // just the filename
}

<p><input type=file name=image onchange="updateFilename(this.value)"></p>
<p>The name of the file you picked is: <span id="filename">(none)</span></p>
<script>
 function updateFilename(path) {
   var name = extractFilename(path);
   document.getElementById('filename').textContent = name;
 }
</script>

4.10.5.1.18 Submit Button state (type=submit)

When an input element's type attribute is in the Submit Button state, the rules in this section apply.

The input element represents a button that, when activated, submits the form. If the element has a value attribute, the button's label must be the value of that attribute; otherwise, it must be an implementation-defined string that means "Submit" or some such. The element is a button, specifically a submit button.

Since the default label is implementation-defined, and the width of the button typically depends on the button's label, the button's width can leak a few bits of fingerprintable information. These bits are likely to be strongly correlated to the identity of the user agent and the user's locale.

The element's input activation behavior given event is as follows:

1. If the element does not have a form owner, then return.

2. If the element's node document is not fully active, then return.

3. Submit the element's form owner from the element with userInvolvement set to event's user navigation involvement.

The formaction, formenctype, formmethod, formnovalidate, and formtarget attributes are attributes for form submission.

The formnovalidate attribute can be used to make submit buttons that do not trigger the constraint validation.