Within operator was implemented in RasMol

src/mol-script/transpilers/helper.ts

src/mol-script/transpilers/rasmol/macroproperties.ts

src/mol-script/transpilers/rasmol/operators.ts

src/mol-script/transpilers/rasmol/parser.ts

src/mol-script/transpilers/rasmol/special_keywords.ts

src/mol-script/transpilers/rasmol/special_operators.ts

src/mol-script/transpilers/rasmol/symbols.ts