attrvalue

Attrvalue is the value assigned to an attribute of an element in markup languages such as HTML and XML. An attribute consists of a name and a value, providing extra information about the element, such as a hyperlink target, an identifier, or presentation hints. The attrvalue is used by user agents and processing tools to influence rendering, behavior, or data handling.

Syntax and quoting rules vary by language. In XML, attribute values must be quoted with either double or single quotes and can include entity references that the parser expands. In HTML, attribute values may be quoted or, in some cases, unquoted if they do not contain prohibited characters; boolean attributes may appear with no explicit value, with the presence of the attribute indicating truth.

Data types and constraints also differ. In XML, an attribute value is conceptually a string, but its allowed form can be constrained by a document type definition or schema, which may specify types such as CDATA, ID, IDREF, NMTOKEN, or others. In HTML, attribute values are strings whose interpretation depends on the attribute and element, with some attributes having specific expected formats (such as URLs or color values).

Examples illustrate common usage. In HTML: <a href="https://example.com" title="Example site">Example</a> has two attrvalues, "https://example.com" and "Example site." In XML: <book id="b001" language="en"> has attrvalues "b001" and "en" for the id and language attributes, respectively.

Security and best practices emphasize treating attrvalues as potentially user-supplied input. Always escape or validate them when constructing markup programmatically to prevent injection and parsing errors.