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In HTML syntax, an attribute is added to a HTML start tag. Several basic attributes types have been recognized, including: (1) required attributes needed by a particular element type for that element type to function correctly; (2) optional attributes used to modify the default functionality of an element type; (3) standard attributes supported ...
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.
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 >.
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.
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.
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.
W3Schools also publishes free HTML templates. It is run by Refsnes Data in Norway. [6] It has an online text editor called TryIt Editor, and readers can edit examples and run the code in a test environment. The website also offers free hosting for small static websites.
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.