Uniform Resource Identifier - Syntax

Syntax

The URI syntax consists of a URI scheme name (such as "http", "ftp", "mailto", "crid" or "file") followed by a colon character, and then by a scheme-specific part. The specifications that govern the schemes determine the syntax and semantics of the scheme-specific part. However, URI syntax does require all schemes to adhere to a general syntax that (among other things) reserves certain characters for special purposes (without always identifying those purposes). The URI syntax also enforces restrictions on the scheme-specific part in order to (for example) provide for a degree of consistency when the part has a hierarchical structure.

Percent encoding can add extra information to a URI.