sign_ = [+ ] => [[ '[ dup first CHAR: - = [ _ prefix ] unless ] ]]
sign = (sign_)? => [[ [ ] or ]]
-width_ = "." ([0-9])* => [[ second >digits '[ _ cramp head ] ]]
+width_ = "." ([0-9])* => [[ second >digits '[ _ bound head ] ]]
width = (width_)? => [[ [ ] or ]]
digits_ = "." ([0-9])* => [[ second >digits ]]