erc-complete-functions

erc-complete-functions is a variable defined in `erc.el'.
Its value is

(erc-pcompletions-at-point erc-button-next-function)

Original value was

• This variable may be risky if used as a file-local variable.

Documentation:
These functions get called when the user hits TAB in ERC.
Each function in turn is called until one returns non-nil to
indicate it has handled the input.

You can customize this variable.