A category filter.
You can query on multiple categories by listing multiple categories separated by slashes. The service returns all entries that match all of the categories (like using AND between terms). For example: <userinput>Fritz/Laurie</userinput> returns entries that match both categories ("Fritz" and "Laurie").
To do an OR between terms, use a pipe character (<literal>|</literal>). For example: <userinput>Fritz%7CLaurie< /userinput> returns entries that match either category.
An entry matches a specified category if the entry is in a category that has a matching term or label, as defined in the Atom specification. (Roughly, the "term" is the internal string used by the software to identify the category, while the "label" is the human-readable string presented to a user in a user interface.)
To exclude entries that match a given category, use the form <userinput>-categoryname</userinput>.
To query for a category that has a scheme – such as <literal><category scheme="urn:google.com" term="public"/>< /literal> – you must place the scheme in curly braces before the category name. For example: <userinput>{urn:google.com}public </userinput>. To match a category that has no scheme, use an empty pair of curly braces. If you don't specify curly braces, then categories in any scheme will match.
The above features can be combined. For example: <userinput>A|-{urn:google.com}B/-C</userinput> means (A OR (NOT B)) AND (NOT C).