Overview#URI Query The query is an optional part, separated by a question mark ("?"), that contains additional identification information that is not hierarchical in nature. The syntax of the query string is not well defined; however by convention it is most often a sequence of <key>=<value> pairs separated by a semicolon or an ampersand. RFC 7320 states that the presence, format and semantics of the query component of URIs is dependent upon many factors, and MAY be constrained by a URI Scheme definition.
Often, they are determined by the implementation of a resource itself.
Applications MUST NOT directly specify the syntax of queries, as this can cause operational difficulties for deployments that do not support a particular form of a query.
For example, a site may wish to support an application using "static" files that do not support query parameters.
Extensions MUST NOT constrain the format or semantics of queries.
For example, an extension that indicates that all query parameters with the name "sig" indicate a cryptographic signature would collide with potentially preexisting query parameters on sites and lead clients to assume that any matching query parameter is a signature.
HTML W3C.REC-html401-19991224 constrains the syntax of query strings used in form submission. New form languages SHOULD NOT emulate it, but instead allow creation of a broader variety of URIs (e.g., by allowing the form to create new path components, and so forth).