of the keys in @code{completion-category-overrides}, the usual
completion behavior is overridden. @xref{Completion Variables}.
+@cindex @code{annotation-function}, in completion
@item annotation-function
The value should be a function for @dfn{annotating} completions. The
function should take one argument, @var{string}, which is a possible
the @code{completions-annotations} face is added by default to
that string.
+@cindex @code{affixation-function}, in completion
@item affixation-function
The value should be a function for adding prefixes and suffixes to
completions. The function should take one argument,
a suffix displayed after the completion string. This function
takes priority over @code{annotation-function}.
+@cindex @code{group-function}, in completion
@item group-function
The value should be a function for grouping the completion candidates.
The function must take two arguments, @var{completion}, which is a
transformed candidate. The transformation can for example remove a
redundant prefix, which is displayed in the group title.
+@cindex @code{display-sort-function}, in completion
@item display-sort-function
The value should be a function for sorting completions. The function
should take one argument, a list of completion strings, and return a
sorted list of completion strings. It is allowed to alter the input
list destructively.
+@cindex @code{cycle-sort-function}, in completion
@item cycle-sort-function
The value should be a function for sorting completions, when
@code{completion-cycle-threshold} is non-@code{nil} and the user is