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HTML attributes are special words used inside the opening tag to control the element's behaviour. It is a piece of markup language used to adjust the behavior or ...
HTML markup consists of several key components, including those called tags (and their attributes), character-based data types, character references and entity references. HTML tags most commonly come in pairs like < h1 > and </ h1 >, although some represent empty elements and so are unpaired, for example < img >.
HTML attributes define desired behavior or indicate additional element properties. Most attributes require a value. In HTML, the value can be left unquoted if it does not include spaces (attribute=value), or it can be quoted with single or double quotes (attribute='value' or attribute="value"). In XML, those quotes are required.
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.
The meta element has two uses: either to emulate the use of an HTTP response header field, or to embed additional metadata within the HTML document. 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.
For these reasons, and in support of a more semantic web, attributes attached to elements within HTML should describe their semantic purpose, rather than merely their intended display properties in one particular medium.
In HTML DOM (Document Object Model), every element is a node: [4] A document is a document node. All HTML elements are element nodes. All HTML attributes are attribute nodes. Text inserted into HTML elements are text nodes. Comments are comment nodes.
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.