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    attr

    Summary

    The attr() CSS function is used to retrieve the value of an attribute of the selected element and use it in the style sheet. It can be used on pseudo-elements too and, in this case, the value of the attribute on the pseudo-element's originated element is returned.

    The attr() function can be used with any CSS property, but support for properties other than content is .

    Syntax

    Formal syntax: attr( attribute-name <type-or-unit>? [, <fallback> ]? )
    

    Values

    attribute-name
    Is the name of an attribute on the HTML element referenced in the CSS.
    <type-or-unit>
    Is a keyword representing either the type of the attribute's value, or its unit, as in HTML some attributes have implicit units. If the use of <type-or-unit> as a value for the given attribute is invalid, the attr() expression will be invalid too. If omitted, it defaults to string. The list of valid values are:
    Keyword Associated type Comment Default value
    string <string> The attribute value is treated as a CSS <string>.  It is NOT reparsed, and in particular the characters are used as-is instead of CSS escapes being turned into different characters. An empty string
    color <color> The attribute value is parsed as a hash (3- or 6-value hash) or a keyword. It must be a valid CSS <string> value.
    Leading and trailing spaces are stripped.
    currentColor
    url <uri></uri> The attribute value is parsed as a string that is used inside a CSS url()function.
    Relative URL are resolved relatively to the original document, not relatively to the style sheet.
    Leading and trailing spaces are stripped.
    The url about:invalid that points to a non-existent document with a generic error condition.
    integer <integer> The attribute value is parsed as a CSS <integer>. If it is not valid, that is not an integer or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0, or, if 0 is not a valid value for the property, the property's minimum value.
    number <number> The attribute value is parsed as a CSS <number>. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0, or, if 0 is not a valid value for the property, the property's minimum value.
    length <length> The attribute value is parsed as a CSS <length> dimension, that is including the unit (e.g. 12.5em). If it is not valid, that is not a length or out of the range accepted by the CSS property, the default value is used.
    If the given unit is a relative length, attr()computes it to an absolute length.
    Leading and trailing spaces are stripped.
    0, or, if 0 is not a valid value for the property, the property's minimum value.
    em, ex, px, rem, vw, vh, vmin, vmax, mm, cm, in, pt, or pc <length> The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as a <length> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
    If the given unit is a relative length, attr()computes it to an absolute length.
    Leading and trailing spaces are stripped.
    0, or, if 0 is not a valid value for the property, the property's minimum value.
    angle <angle> The attribute value is parsed as a CSS <angle> dimension, that is including the unit (e.g. 30.5deg). If it is not valid, that is not an angle or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0deg, or, if 0deg is not a valid value for the property, the property's minimum value.
    deg, grad, rad <angle> The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as an <angle> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0deg, or, if 0deg is not a valid value for the property, the property's minimum value.
    time <time> The attribute value is parsed as a CSS <time> dimension, that is including the unit (e.g. 30.5ms). If it is not valid, that is not a time or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0s, or, if 0s is not a valid value for the property, the property's minimum value.
    s, ms <time> The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as an<time> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0s, or, if 0s is not a valid value for the property, the property's minimum value.
    frequency <frequency> The attribute value is parsed as a CSS <frequency> dimension, that is including the unit (e.g. 30.5kHz). If it is not valid, that is not a frequency or out of the range accepted by the CSS property, the default value is used. 0Hz, or, if 0Hz is not a valid value for the property, the property's minimum value.
    Hz, kHz <frequency> The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as a <frequency> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
    Leading and trailing spaces are stripped.
    0Hz, or, if 0Hz is not a valid value for the property, the property's minimum value.
    % <percentage> The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as a <percentage>. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
    If the given value is used as a length, attr()computes it to an absolute length.
    Leading and trailing spaces are stripped.
    0%, or, if 0% is not a valid value for the property, the property's minimum value.
    <fallback>
    The value to be used if the associated attribute is missing or contains an invalid value. The fallback value must be valid where attr() is used, even if it is not used, and must not contain another attr() expression. If attr() is not the sole component value of a property, its <fallback> value must be of the type defined by <type-or-unit>. If not set, CSS will use the default value defined for each <type-or-unit>.

    Examples

    p::before {
      content: attr(data-foo) " ";
    }
    
    <p data-foo="hello">world</p>
    

    Result

    Specifications

    Specification Status Comment
    CSS Values and Units Module Level 3
    The definition of 'attr()' in that specification.
    Candidate Recommendation Added two optional parameters; can be used on all properties; may return other values than <string>. These changes are experimental and may be dropped during the CR phase if browser support is too small.
    CSS Level 2 (Revision 1)
    The definition of 'attr()' in that specification.
    Recommendation Limited to the content property; always return a <string>.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 2.0 1.0 (1.7 or earlier) 8 9.0 3.1
    Usage in other properties than content and with non-string values  Not supported Not supported (see bug 435426) Not supported ? ?
    Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support 2.1 1.0 (1.0) 8 10.0 3.1
    Usage in other properties than contentand with non-string values  ? Not supported (see bug 435426) Not supported ? ?

     

    Document Tags and Contributors

    Last updated by: jwhitlock,