Compare the first image in the README to the corresponding section of the "original grammar":

  if_stmt:
      | 'if' named_expression ':' block elif_stmt 
      | 'if' named_expression ':' block [else_block] 
  elif_stmt:
      | 'elif' named_expression ':' block elif_stmt 
      | 'elif' named_expression ':' block [else_block] 
  else_block:
      | 'else' ':' block 

Whilst I can read this, I need to jump around to find the definitions of labels, and it requires mental effort to remember how each label was defined. The effort would be greater for a more complex example.

The diagram essentially avoids this by inlining the definitions of `elif_stmt` and `else_block`. This makes it much faster for me to read.