erc-input-ring-index

erc-input-ring-index is a variable defined in `erc-ring.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Position in the input ring for erc.
If nil, the input line is blank and the user is conceptually 'after'
the most recently added item in the ring. If an integer, the input
line is non-blank and displays the item from the ring indexed by this
variable.