[PHP 8.3] Added json_validate function description.

[mumumu]

Based on RFC and json_validate source code.

[TimWolla]

<para>
 Returns whether the given &string; is syntactically valid JSON.
 If <function>json_validate</function> returns &true;, <function>json_decode</function>
 will successfully decode the given string when using the same
 <parameter>depth</parameter> and <parameter>flags</parameters>.
</para>
<para>
 If <function>json_validate</function> returns &false;, the cause
 can be retrieved using <function>json_last_error</function> and
 <function>json_last_error_msg</function>.
</para>
<para>
 <function>json_validate</function> uses less memory than
 <function>json_decode</function> if decoded JSON payload is
 not used, because it does not need to build the array or
 object structure containing the payload.
</para>
<caution>
 <para>
  Calling <function>json_validate</function> immediately before
  <function>json_decode</function> will unnecessarily parse the string
  twice, as <function>json_decode</function> implicitly performs
  validation during decoding.
 </para>
 <para>
  <function>json_validate</function> should therefore only be used
  if the decode JSON payload is not immediately used and knowing whether
  the string contains valid JSON is needed.
 </para>
</caution>

[Girgias]

Small nit to the above suggestion:

json_validate uses less memory than
json_decode if the decoded JSON payload is
not used, because it does not need to build the array or
object structure containing the payload.

[Girgias]

This is confusing?

Should be a bitmask of JSON_* constatns no?

[mumumu]

It seems that json_validate accepts PHP_JSON_INVALID_UTF8_IGNORE only.

	if ((options != 0) && (options != PHP_JSON_INVALID_UTF8_IGNORE)) {
		zend_argument_value_error(3, "must be a valid flag (allowed flags: JSON_INVALID_UTF8_IGNORE)");
		RETURN_THROWS();
	}

https://github.com/php/php-src/blob/ea299d44a155e0ef39c24a4d79b0e51accf8d9d0/ext/json/json.c#L329-L332

We should change as the following?

    <varlistentry>
     <term><parameter>flags</parameter></term>
     <listitem>
      <para>
       Currently only 
       <constant>JSON_INVALID_UTF8_IGNORE</constant>
       is accepted.
      </para>
     </listitem>
    </varlistentry>

[Girgias]

Yes I think this makes more sense. :)

[Girgias]

Mostly agree with @TimWolla's suggestions

[TimWolla]

LGTM now, except for Girgias' remark regarding the flags parameter.