"If non-nil, allow effects in `pcomplete-parse-arguments-function'.
For the `pcomplete' command, it was common for functions in
`pcomplete-parse-arguments-function' to make modifications to the
-buffer, like expanding variables are such.
+buffer, like expanding variables and such.
For `completion-at-point-functions', this is not an option any more, so
this variable is used to tell `pcomplete-parse-arguments-function'
whether it can do the modifications like it used to, or whether