bug#24073: 24.5; outline-on-heading-p sees any invisible text property as outline inviisble

[Paul Rankin]

Eli Zaretskii <eliz@gnu.org> on Tue, 26 Jul 2016 18:14 +0300:
> For outline's own use, sure.  But this function is also used by Org,
> so I think we need to coordinate with Org developers about such a
> change, to make sure we don't break Org in the process.

I'll leave this in your hands.

> Btw, can you describe the real-life use case where you bumped into
> this issue?

I author a major mode for a format wherein some outline headings are prefixed 
with a non-printing "forced" character.

I've given the user the option to hide these non-printing "forced" characters 
by adding an invisible text property and keyword to the regexp group (the 
"forced" character), then using `add-to-invisibility-spec' to add that keyword.

The invisible property is managed by Font Lock.

It will probably not shed any further light, but here is the real-life code:
https://github.com/rnkn/fountain-mode/blob/0707b4753fabdc07cbe04030b1559671d87c57f2/fountain-mode.el#L3691-L3699