Rule 2-5-1

[ogawa.kiyoshi]

I feel, the sentence "The use of digraphs may not meet developer expectations." is not clear.
The usage of digraphs are only system constraints.
Digraph are just an alternative method for a systems that can not input '{','}','[',']'.
Therefore, there is no point in leaving a digraph in the final source file.
Even if anyone use a system that requires digraphs, it is better to replace in the final source file from digraph(alternative token) to primary token.