16.5.1 Autoload by Prefix

During completion for the commands describe-variable and describe-function, Emacs will try to load files which may contain definitions matching the prefix being completed. The variable definition-prefixes holds a hashtable which maps a prefix to the corresponding list of files to load for it. Entries to this mapping are added by calls to register-definition-prefixes which are generated by loaddefs-generate (see Autoload). Files which don’t contain any definitions worth loading (test files, for example), should set autoload-compute-prefixes to nil as a file-local variable.