PHP RFC: Trim Form Feed

• Version: 1.0
• Date: 2025-12-28
• Author: Weilin Du, lamentxu@163.com
• Status: Draft
• Implementation: https://github.com/php/php-src/pull/20788

The trim(), ltrim(), and rtrim() functions strip whitespace (or other characters) from the beginning and/or 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().

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 string.whitespace).
• JavaScript: String.prototype.trim() removes \f (defined as White_Space in ECMA-262, see MDN Web Docs).
• Rust: str::trim() removes \f (based on Unicode White_Space property, see std::primitive::str::trim).
• Go: strings.TrimSpace() removes \f (see strings.TrimSpace).

// 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"

Scripts that rely on trim() preserving leading or trailing Form Feed characters will be affected.

PHP 8.6

• Pull Request: GH-20788
• Issue: GH-20783

* Internal discussion