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Where element names the HTML element type, and attribute is the name of the attribute, set to the provided value. The value may be enclosed in single or double quotes, although values consisting of certain characters can be left unquoted in HTML (but not XHTML). [2] [3] Leaving attribute values unquoted is considered unsafe. [4]
HTML defines several data types for element content, such as script data and stylesheet data, and a plethora of types for attribute values, including IDs, names, URIs, numbers, units of length, languages, media descriptors, colors, character encodings, dates and times, and so on. All of these data types are specializations of character data.
In SGML, HTML and XML documents, the logical constructs known as character data and attribute values consist of sequences of characters, in which each character can manifest directly (representing itself), or can be represented by a series of characters called a character reference, of which there are two types: a numeric character reference and a character entity reference.
With HTML up to and including HTML 4.01 and XHTML, there were four valid attributes: content, http-equiv, name and scheme. Under HTML 5, charset has been added and scheme has been removed. http-equiv is used to emulate an HTTP header, and name to embed metadata. The value of the statement, in either case, is contained in the content attribute ...
Element (and attribute) names may be written in any combination of upper or lower case in HTML, but must be in lower case in XHTML. [8] The canonical form was upper-case until HTML 4 , and was used in HTML specifications, but in recent years, lower-case has become more common.
Incorrect HTML entity escaping may also open up security vulnerabilities for injection attacks such as cross-site scripting. If HTML attributes are left unquoted, certain characters, most importantly whitespace, such as space and tab, must be escaped using entities. Other languages related to HTML have their own methods of escaping characters.
HTML attribute. alt attribute; HTML frame; HTML editor; Character encodings. named characters; ... and introduces a more appropriate class name. By the correct use of ...
The role attribute is used to define an element's role on a page. When sectioning elements were introduced, the role attribute became used less for landmarking. This is because roles were applied by default to most sectioning elements, therefore, they were more widely used and accepted for their simplicity.