@9: Make index entry (user-defined format)

The construction @9Text@> is used to create an index entry in a format defined by the user. It is associated with the macro \9, which will be called during TeX's processing of the Index as \9{Text}. The user must define \9 according to the format

     \def\9#1{...}
     

where argument #1 is the text between @9 and @>. For example, to print that text in a sans serif font, say

     \def\9#1{{\sf #1}}
     

(Note the extra level of braces to prevent the font command from propagating.)