erc-server-processing-p

erc-server-processing-p is a variable defined in `erc-backend.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Non-nil when we're currently processing a message.

When ERC receives a private message, it sets up a new buffer for
this query. These in turn, though, do start flyspell. This
involves starting an external process, in which case Emacs will
wait - and when it waits, it does accept other stuff from, say,
network exceptions. So, if someone sends you two messages
quickly after each other, ispell is started for the first, but
might take long enough for the second message to be processed
first.