docs: def p_startswith(self, st, ignorecase=False):
          "Return True if the input starts with `st` at current position"
          length = len(st)
          matcher = result = self.input[self.pos:self.pos + length]
          if ignorecase:
              matcher = result.lower()
              st = st.lower()
          if matcher == st:
              self.pos += length
              return result
          return False