====== PHP RFC: Add Form Feed in Trim Functions ======
  * Version: 1.0
  * Date: 2025-12-28
  * Author: Weilin Du, lamentxu@163.com
  * Status: Under Discussion
  * Implementation: https://github.com/php/php-src/pull/20788

===== Introduction =====
The ''trim()'', ''ltrim()'', and ''rtrim()'' functions strip whitespace (or other characters) from the beginning and end of a string. When the second parameter (''$characters'') is omitted, these functions use a default set of characters.

Currently, this default set includes:
  * ''" "'' (ASCII 32 (0x20)), an ordinary space.
  * ''"\t"'' (ASCII 9 (0x09)), a tab.
  * ''"\n"'' (ASCII 10 (0x0A)), a new line (line feed).
  * ''"\r"'' (ASCII 13 (0x0D)), a carriage return.
  * ''"\0"'' (ASCII 0 (0x00)), the NUL-byte.
  * ''"\v"'' (ASCII 11 (0x0B)), a vertical tab.

Notably missing from this list is ''"\f"'' (ASCII 12 (0x0C)), the **Form Feed** character.

This RFC proposes adding ''"\f"'' to the default list of characters stripped by ''trim()'', ''ltrim()'', and ''rtrim()''.

===== Proposal =====
The proposal is to include the Form Feed character (''\f'' / ''0x0C'') in the default character mask for ''trim()'', ''ltrim()'', and ''rtrim()''. Most modern programming languages treat ''\f'' as whitespace in their trimming functions. Aligning PHP with this behavior reduces cognitive load for developers working in polyglot environments.

The Form Feed character is widely recognized as whitespace.
  * **C Standard / POSIX:** The ''isspace()'' function in ''libc'' (which PHP relies on internally) defines ''\f'' as a whitespace character.
  * **PHP Internals:** Other PHP functions such as ''is_numeric()'' already treat ''\f'' as whitespace when parsing strings.
  * **Python:** ''str.strip()'' removes ''\f'' by default (defined in [[https://docs.python.org/3/library/string.html#string.whitespace|string.whitespace]]).
  * **JavaScript:** ''String.prototype.trim()'' removes ''\f'' (defined as ''White_Space'' in ECMA-262, see [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trim|MDN Web Docs]]).
  * **Rust:** ''str::trim()'' removes ''\f'' (based on Unicode ''White_Space'' property, see [[https://doc.rust-lang.org/std/primitive.str.html#method.trim|std::primitive::str::trim]]).
  * **Go:** ''strings.TrimSpace()'' removes ''\f'' (see [[https://pkg.go.dev/strings#TrimSpace|strings.TrimSpace]]).

==== Examples ====
<PHP>
<?php

// Current Behavior
$str = "\fHello World\f";
var_dump(trim($str));
// string(13) "\fHello World\f"

// Proposed Behavior
$str = "\fHello World\f";
var_dump(trim($str));
// string(11) "Hello World"

?>
</PHP>

===== Backward Incompatible Changes =====
This is a **backward incompatible change**. Scripts that rely on ''trim()'' //preserving// leading or trailing Form Feed characters will be affected.

===== Proposed PHP Version(s) =====
PHP 8.6

===== RFC Impact =====
==== To the Ecosystem ====
There are several impacts to the ecosystem (mostly minor impacts):
  * **IDEs and Language Servers:** These tools will need to update their documentation (tooltips) for ''trim'', ''ltrim'', and ''rtrim'' to include ''\f'' in the list of default stripped characters.
  * **Static Analyzers:** These tools may need to update their internal return type inference logic. For example, ''trim("\f")'' currently results in a non-empty string, but under this proposal, it will result in an empty string. Updating their internal stubs will ensure accurate analysis.
  * **Polyfills:** Libraries that provide polyfills for string functions might need to be aware of this change, although polyfilling a change to a default parameter value in a core function is generally not done for minor versions.

==== To Existing Extensions ====
Existing extensions should not require recompilation.

==== To SAPIs ====
There is no specific impact on any SAPI (CLI, FPM, Apache, etc.). The change is limited to the string manipulation logic within the standard library.

===== Open Issues =====
Currently no open issues ongoing.

===== Future Scope =====
This RFC only focus on php function ''trim'', ''ltrim'' and ''rtrim'' but not on other trimming functions implemented in php (such as in php filters).

Also, in the future there may be a new discussion about removing the NULL character (ASCII 0) from the default list of characters stripped by ''trim'', ''ltrim'' and ''rtrim'' in a separated RFC.

===== Voting Choices =====
The voting will start after the cool-down period (expected 3 weeks, at Sat 18th Jan 2026 if no new issue(s) is raised).

----

Primary Vote requiring a 2/3 majority to accept the RFC:

<doodle title="Add form feed in trim, ltrim and rtrim default character mask as outlined in the RFC?" voteType="single" closed="true" closeon="2025-01-01T15:30:00Z">
   * Yes
   * No
   * Abstain
</doodle>

===== Patches and Tests =====
  * **Pull Request:** [[https://github.com/php/php-src/pull/20788|GH-20788]]
  * **Issue:** [[https://github.com/php/php-src/issues/20783|GH-20783]]

===== Implementation =====
The RFC hasn't been accepted yet.

===== References =====
* [[https://news-web.php.net/php.internals/129706|Internal discussion]]

===== Rejected Features =====
None for now.

===== Changelog =====
2025/12/29: Initial version.
2025/12/29: Change typos and expressions, also title.