I suppose one alternative solution might be to tweak the ELLIPSIS feature of doctest, such that it would interpret a run of >=3 periods in a row (matching regex pattern of "[.]{3,}") as 'ellipsis'.

The regex for PS2 could then have a negative lookahead added, so that it *only* matches three periods, plus optionally other content: '\.\.\.(?!\.)'

That way, a line like "... foo" would retain the current meaning of "'source' line, consisting of PS2 plus the identifier 'foo'", but the meaning of "arbitrary content followed by ' foo'" could be achieved by ".... foo", since the leading "...." would NOT match the negative lookahead for PS2.

In other situations, where "..." is *not* the leading non-whitespace content, the old behavior suffices: the PS2 regex won't match anyways, so it'll be left for ELLIPSIS to process.