System for computing and rendering differences between two text strings, commonly used for revision comparison.

Since: 2.6.0
Source: wp-includes/wp-diff.php, wp-includes/pluggable.php

Components

Architecture

WordPress uses the PEAR Text_Diff library as its foundation, with custom renderers for WordPress-specific HTML output.

wp_text_diff()
    ├── normalize_whitespace() - Clean input strings
    ├── Text_Diff - PEAR library computes diff operations
    └── WP_Text_Diff_Renderer_Table
            ├── _added() / _deleted() / _context()
            └── _changed()
                    └── WP_Text_Diff_Renderer_inline
                            └── Word-by-word highlighting

PEAR Text_Diff Components

WordPress bundles these PEAR library files:

Usage

Basic Comparison

$old = "The quick brown fox";
$new = "The quick red fox";

$diff = wp_text_diff( $old, $new );
// Returns HTML table showing "brown" deleted, "red" added

With Titles

$diff = wp_text_diff( $old, $new, array(
    'title'       => 'Content Comparison',
    'title_left'  => 'Original',
    'title_right' => 'Modified',
) );

Single Column View

$diff = wp_text_diff( $old, $new, array(
    'show_split_view' => false,
) );

Output Structure

The diff output is an HTML table with accessible markup:

<table class="diff is-split-view">
    <caption class="diff-title">Title</caption>
    <thead>
        <tr class="diff-sub-title">
            <th>Original</th>
            <th>Modified</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td class="diff-deletedline">
                <span class="dashicons dashicons-minus"></span>
                <span class="screen-reader-text">Deleted:</span>
                old text with <del>removed</del>
            </td>
            <td class="diff-addedline">
                <span class="dashicons dashicons-plus"></span>
                <span class="screen-reader-text">Added:</span>
                new text with <ins>added</ins>
            </td>
        </tr>
    </tbody>
</table>

CSS Classes

Core Usage

WordPress uses this system for:

• Post Revisions — Comparing revision content in the admin
• Plugin/Theme Editor — Showing file changes before saving
• Customizer — Comparing customizer settings
• Import/Export — Displaying content differences

Diff Threshold

When comparing changed lines, word-level diffs are only shown if the lines are similar enough (< 60% different). This prevents confusing output when lines are completely rewritten.

// In WP_Text_Diff_Renderer_Table
protected $_diff_threshold = 0.6;

Related Functions