Every possible string a grammar generates is assigned a probability weight formula_11 given the PCFG model formula_12. It follows that the sum of all probabilities to all possible grammar productions is formula_13. The scores for each paired and unpaired residue explain likelihood for secondary structure formations. Production rules also allow scoring loop lengths as well as the order of base pair stacking hence it is possible to explore the range of all possible generations including suboptimal structures from the grammar and accept or reject structures based on score thresholds.