doc: improve PG 12 to_timestamp()/to_date() wording

doc/src/sgml/func.sgml

@@ -6388,7 +6388,7 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
 
      <listitem>
       <para>
-       A separator (a space or a non-letter/non-digit character) in the template string of
+       A separator (a space or non-letter/non-digit character) in the template string of
        <function>to_timestamp</function> and <function>to_date</function>
        matches any single separator in the input string or is skipped,
        unless the <literal>FX</literal> option is used.
@@ -6399,22 +6399,22 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
        exceeds the number of separators in the template.
       </para>
       <para>
-       If <literal>FX</literal> is specified, separator in template string
-       matches to exactly one character in input string.  Notice we don't insist
-       input string character to be the same as template string separator.
+       If <literal>FX</literal> is specified, a separator in the template string
+       matches exactly one character in input string.  Notice we don't insist the
+       input string character be the same as the template string separator.
        For example, <literal>to_timestamp('2000/JUN', 'FXYYYY MON')</literal>
        works, but <literal>to_timestamp('2000/JUN', 'FXYYYY&nbsp;&nbsp;MON')</literal>
-       returns an error because a space second template string space consumed
-       letter <literal>J</literal> from the input string.
+       returns an error because the second template string space is consumed
+       by the letter <literal>J</literal> in the input string.
       </para>
      </listitem>
 
      <listitem>
       <para>
-       <literal>TZH</literal> template pattern can match a signed number.
-       Without the <literal>FX</literal> option, it may lead to ambiguity in
+       A <literal>TZH</literal> template pattern can match a signed number.
+       Without the <literal>FX</literal> option, it can lead to ambiguity in
        interpretation of the minus sign, which can also be interpreted as a separator.
-       This ambiguity is resolved as follows.  If the number of separators before
+       This ambiguity is resolved as follows:  If the number of separators before
        <literal>TZH</literal> in the template string is less than the number of
        separators before the minus sign in the input string, the minus sign
        is interpreted as part of <literal>TZH</literal>.