What does this mean (lookupflag IgnoreMarks;)?

It says in Glyphs that I have an error message in features.
How do I figure out the error? In features I saw this code (lookupflag IgnoreMarks;).
What does it mean?

  • Which Glyphs version exactly?
  • What exactly is the error message?

I am using Glyphs 3. I figured out what was wrong. I had added a symbol as a new Glyph instead of adding it from the sidebar menu.

That shouldn’t matter, unless you had an illegal glyph name.

What name did you use for that manually added glyph?

I named the glyph | for the bar symbol. I figured out that was the problem because I started deleting the last few glyphs I created to find the problem and after I deleted this glyph the error message went away.

How did you manage to use that glyph name? The app should prevent this.

Somehow I was able to.