2.2.3.6.2 Custom Query Options
Custom query options provide an extensible mechanism for data service-specific information to be placed in a data service URI query string. A custom query option is any query option of the form shown by the rule "customQueryOption" in URI Syntax (section 2.2.3.1). Custom query options MUST NOT begin with a "$" character because the character is reserved for system query options, as described in System Query Options (section 2.2.3.6.1).