I added my patch, which I've been using for several months. It seems to work fine and marks are accepted anywhere on the line, not only at the beginning.

Please treat this only as the idea of the way I changed folding.el. Actual patch will be made cleaner and probably wrapped into a setting variable. Perhaps some users prefer to limit marks usage to the beginning of a line.

I still experience one issue: the opening mark is ignored if put on the first line. I will have to fix this, when the patch will have a chance of acceptation.

Seems like the fold markers are active only when they are placed at the beginning of a line. If this is a feature, then please document it. I read the documentation and couldn't find any remark about it.

Since in jEdit text editor such marks may be placed anywhere on the line, I was strongly confused by folding.el behaviour. Wasted some time before discovering the need to place the mark at line start.