I suggest to clarify the documentation of PQconninfoParse().
First, "Returns parsed connection options from the provided connection string." Its false. The returned array contains all options, rather than which only parsed from the provided connection string. This fact must be specified in the documentation becase the name of the function mismatches its behaviour.
Second, "Note that only options explicitly specified in the string will have values set in the result array; no defaults are inserted." Its true. But instead of "no defaults are inserted" I suggest "values of other options will have NULL values."