Use underscore for underline.

[ingydotnet]

Underscores are almost never used in plain prose sentences. So single _ can be used to underline.

I _love_ pie.

This markup likely is missing in many backend markups like markdown and pod. That's OK because Kwim wants to be a superset anyway.

@pdl, any thoughts?

[ingydotnet]

We can still use this

_____

To be a different "fill-in-the-blank" markup that is 5 wide (since no prose chars are involved).

[pdl]

If you plan to use kwim for writing about code, consider situations where you might talk have three_word_variables or internal _method calls

Some markups use _ for italic, kwim uses / for this, so that's ok.

[ingydotnet]

added