substring synopsis section, third argument is optional doc didn't show that

hi.
https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-SIMILARTO-REGEXP

"""
or as a plain three-argument function:
substring(string, pattern, escape-character)
"""

but here "escape-character" is optional.


substring(string, pattern [,escape-character])
would be more accurate.
then we may also need to rephrase
"or as a plain three-argument function:"