perlapi: Rewrite pod for grok_number, combine with _flags

I found the old version overly confusing.

numeric.c

@@ -975,36 +975,62 @@ Perl_grok_infnan(pTHX_ const char** sp, const char* send)
 }
 
 /*
-=for apidoc grok_number_flags
-
-Recognise (or not) a number.  The type of the number is returned
-(0 if unrecognised), otherwise it is a bit-ORed combination of
-C<IS_NUMBER_IN_UV>, C<IS_NUMBER_GREATER_THAN_UV_MAX>, C<IS_NUMBER_NOT_INT>,
-C<IS_NUMBER_NEG>, C<IS_NUMBER_INFINITY>, C<IS_NUMBER_NAN> (defined in perl.h).
-
-If the value of the number can fit in a UV, it is returned in C<*valuep>.
-C<IS_NUMBER_IN_UV> will be set to indicate that C<*valuep> is valid, C<IS_NUMBER_IN_UV>
-will never be set unless C<*valuep> is valid, but C<*valuep> may have been assigned
-to during processing even though C<IS_NUMBER_IN_UV> is not set on return.
-If C<valuep> is C<NULL>, C<IS_NUMBER_IN_UV> will be set for the same cases as when
-C<valuep> is non-C<NULL>, but no actual assignment (or SEGV) will occur.
-
-C<IS_NUMBER_NOT_INT> will be set with C<IS_NUMBER_IN_UV> if trailing decimals were
-seen (in which case C<*valuep> gives the true value truncated to an integer), and
-C<IS_NUMBER_NEG> if the number is negative (in which case C<*valuep> holds the
-absolute value).  C<IS_NUMBER_IN_UV> is not set if C<e> notation was used or the
-number is larger than a UV.
-
-C<flags> allows only C<PERL_SCAN_TRAILING>, which allows for trailing
-non-numeric text on an otherwise successful I<grok>, setting
-C<IS_NUMBER_TRAILING> on the result.
 
+=for apidoc      grok_number
+=for apidoc_item grok_number_flags
+
+Look for a number in the C<len> bytes starting at C<pv>.  If one isn't found,
+return 0; otherwise return its type (and optionally its value).  In
+C<grok_number> all C<len> bytes must be either leading C<L</isSPACE>>
+characters or part of the number.  The same is true in C<grok_number_flags>
+unless C<flags> contains the C<PERL_SCAN_TRAILING> bit, which allows for
+trailing non-numeric text.  (This is the only difference between the two
+functions.)
+
+The returned type is the ORing of various bits (#defined in F<perl.h>) as
+described below:
+
+If the number is negative, the returned type will include the C<IS_NUMBER_NEG>
+bit.
+
+If the absolute value of the integral portion of the found number fits in a UV,
+the returned type will include the C<IS_NUMBER_IN_UV> bit.  If it won't fit,
+instead the C<IS_NUMBER_GREATER_THAN_UV_MAX> bit will be included.
+
+If the found number is not an integer, the returned type will include
+the C<IS_NUMBER_NOT_INT> bit. This happens either if the number
+is expressed in exponential C<e> notation, or if it includes a decimal
+point (radix) character.  If exponential notation is used, then neither
+IS_NUMBER_IN_UV nor IS_NUMBER_GREATER_THAN_UV_MAX bits are set.
+Otherwise, the integer part of the number is used to determine the
+C<IS_NUMBER_IN_UV> and C<IS_NUMBER_GREATER_THAN_UV_MAX> bits.
+
+If the found number is a string indicating it is infinity, the
+C<IS_NUMBER_INFINITY> and C<IS_NUMBER_NOT_INT> bits are included in the
+returned type.
+
+If the found number is a string indicating it is not a number, the
+C<IS_NUMBER_NAN> and C<IS_NUMBER_NOT_INT> bits are included in the
+returned type.
+
+You can get the number's absolute integral value returned to you by calling
+these functions with a non-NULL C<valuep> argument.  If the returned type
+includes the C<IS_NUMBER_IN_UV> bit, C<*valuep> will be set to the correct
+value.  Otherwise, it could well have been zapped with garbage.
+
+In C<grok_number_flags> when C<flags> contains the C<PERL_SCAN_TRAILING>
+bit, and trailing non-numeric text was found, the returned type will include
+the C<IS_NUMBER_TRAILING> bit.
+
+=for apidoc Amnh||IS_NUMBER_GREATER_THAN_UV_MAX
+=for apidoc Amnh||IS_NUMBER_INFINITY
+=for apidoc Amnh||IS_NUMBER_IN_UV
+=for apidoc Amnh||IS_NUMBER_NAN
+=for apidoc Amnh||IS_NUMBER_NEG
+=for apidoc Amnh||IS_NUMBER_NOT_INT
+=for apidoc Amnh||IS_NUMBER_TRAILING
 =for apidoc Amnh||PERL_SCAN_TRAILING
 
-=for apidoc grok_number
-
-Identical to C<grok_number_flags()> with C<flags> set to zero.
-
 =cut
  */
 int