Highlight searched term in content

highlight-search.php

<?php

function get_highlighted_content( $args = array() ) {

	// Setup defaults.
	$defaults = array(
		'content' => get_the_title(),
	);

	// Parse args.
	$args = wp_parse_args( $args, $defaults );

	// Get queried term and force lowercase.
	$search_query = strtolower( get_search_query() );
	// Set list of articles.
	$articles = array( 'in', 'at', 'a', 'an', 'the', 'of', 'and', 'to', 'for', 'into' );

	// Replace list of articles with nothing — does check for exact match.
	$search_query = preg_replace( '/\b(' . implode( '|', $articles ) . ')\b/', '', $search_query );

	// Get content text.
	$content = $args['content'];

	// Split string for loop below by spaces.
	if ( ! is_array( $search_query ) ) {
		$search_query = preg_split( '/ /', $search_query, -1, PREG_SPLIT_NO_EMPTY );
	}

	// Define Pattern and Separator.
	$pattern = '#\\b(\\w*)(';
	$sep = '';

	// Loop throug each word in search query string.
	foreach ( $search_query as $word ) {
		$pattern .= $sep . preg_quote( ' ' . $word, '' );
		$sep = '|';
	}

	// Capture word/word-characters after foreach.
	$pattern .= ')(\\w*)\\b#i';

	// Using \1 \2 \3 at relevant places. Make it so.
	return preg_replace( $pattern, '\\1<strong>\\2</strong>\\3', $content );
}