The "Grammars/gra_nodangle.gap" grammar captures Stefan Wuchty's ideas of describing all possible, nested, secondary structures for a given RNA sequence in a non-redundant way (see Complete suboptimal folding of RNA and the stability of secondary structures or the program RNAsubopt). Dangling bases are not considered. Each hairpin must have at least three unpaired bases in its loop. Bulge loops are restricted to have at most 30 unpaired bases. Both unpaired regions of an internal loop are restricted to a maximal size of 30 bases (in the Vienna package, the sum of both regions might not exceed 30 bases).
Following an idea from splitting the Signature Signatures/sig_foldrna.gap, large parts of commonly used production rules are outsourced into the grammar part file Grammars/Parts/grapart_basic.gap.