class_docstr: Leafs are basically tokens with a better API. Leafs exactly know where they
  were defined and what text preceeds them.
class_docstr_tok: ["Leafs","are","basically","tokens","with","a","better","API",".","Leafs","exactly","know","where","they","were","defined","and","what","text","preceeds","them","."]
code: def get_start_pos_of_prefix(self):
      previous_leaf = self.get_previous_leaf()
      if previous_leaf is None:
          lines = split_lines(self.prefix)
          # + 1 is needed because split_lines always returns at least [''].
          return self.line - len(lines) + 1, 0  # It's the first leaf.
      return previous_leaf.end_pos
  
imports: from abc import abstractmethod, abstractproperty
  from typing import List, Optional, Tuple, Union
  from parso.utils import split_lines
label_desc: Use image node_id 4 for calling the Leaf obj's underlying member method code with example usage: obj.get_start_pos_of_prefix() and returns: previous_leaf, unknown,  int