Inline diff renderer with improved word splitting for multilingual support.

Source: wp-includes/class-wp-text-diff-renderer-inline.php
Since: 2.6.0 (class), 4.7.0 (separate file)
Extends: Text_Diff_Renderer_inline

Purpose

This class improves upon the PEAR Text_Diff_Renderer_inline by providing better word splitting that handles Unicode characters properly. It’s used internally by WP_Text_Diff_Renderer_Table to generate word-level diffs within changed lines.

Properties

Uses #[AllowDynamicProperties] attribute for PHP 8.2+ compatibility.

Methods

_splitOnWords()

Splits a string into an array of words and delimiters for comparison.

public function _splitOnWords( string $string, string $newlineEscape = "n" ): array

Returns: Array of words and delimiter characters.

Improvements Over PEAR

The parent PEAR class uses a simpler word-splitting regex that may not handle Unicode properly. WordPress’s version:

1. Removes null bytes — Strips characters to prevent issues
2. Unicode-aware splitting — Uses /([^w])/u with the u (Unicode) flag
3. Preserves all delimiters — Uses PREG_SPLIT_DELIM_CAPTURE to keep punctuation

Algorithm

// 1. Remove null bytes
$string = str_replace( "", '', $string );

// 2. Split on non-word characters (Unicode-aware)
$words = preg_split( '/([^w])/u', $string, -1, PREG_SPLIT_DELIM_CAPTURE );

// 3. Escape newlines
$words = str_replace( "n", $newlineEscape, $words );

return $words;

Usage

This class is typically not used directly. It’s instantiated by WP_Text_Diff_Renderer_Table::_changed() to compute word-level diffs:

// Inside WP_Text_Diff_Renderer_Table::_changed()
$text_diff = new Text_Diff( 'auto', array( array( $orig_line ), array( $final_line ) ) );
$renderer = new $this->inline_diff_renderer(); // WP_Text_Diff_Renderer_inline
$diff = $renderer->render( $text_diff );

// $diff contains: "The quick <del>brown</del><ins>red</ins> fox"

Output Format

The parent Text_Diff_Renderer_inline class (from PEAR) produces output with <ins> and <del> tags:

The quick <del>brown</del><ins>red</ins> fox jumped

When rendered by WP_Text_Diff_Renderer_Table, this is separated:

• Deleted column: The quick <del>brown</del> fox jumped (with <ins> tags stripped)
• Added column: The quick <ins>red</ins> fox jumped (with <del> tags stripped)

Customizing

To use a different inline renderer, set the property on the table renderer:

class My_Inline_Renderer extends WP_Text_Diff_Renderer_inline {
    public function _splitOnWords( $string, $newlineEscape = "n" ) {
        // Custom word splitting logic
        // Perhaps treating hyphenated words as single units
        $string = str_replace( "", '', $string );
        $words = preg_split( '/(s+|[^w-])/u', $string, -1, PREG_SPLIT_DELIM_CAPTURE );
        $words = str_replace( "n", $newlineEscape, $words );
        return $words;
    }
}

class My_Table_Renderer extends WP_Text_Diff_Renderer_Table {
    protected $inline_diff_renderer = 'My_Inline_Renderer';
}

Unicode Example

// Japanese text comparison
$old = "こんにちは世界";
$new = "こんにちは宇宙";

// WP_Text_Diff_Renderer_inline correctly splits on character boundaries
// Output: こんにちは<del>世界</del><ins>宇宙</ins>

Related Files