GSUB glyph deletion

Is it possible to remove a glyph via a substitution rule using Glyphs? The afdko documentation mentions sub A by NULL;, however this results in the error ‘Unexpected “NULL” in rule substitution’ when I try it in Glyphs (3086).

I understand this is a relatively new addition to the afdko spec — is there a plan to implement it in Glyphs? (Or is it already present under a different syntax?)

See Support glyph deletion in features - #2 by GeorgSeifert.

In the meantime you can use a dummy glyph and give it Mark, Nonspacing category and subcategory, so it would be ignored when IgnoreMarks lookup flag is set.