convert naming convention (PascalCased, camelCased, with_underscores) to each other

NamingConventionConverter.php

<?php
class NamingConventionConverter {

    /**
     * convert camelCasedString or PascalCasedString to underscores_string
     * ref: http://stackoverflow.com/questions/1993721/how-to-convert-camelcase-to-camel-case
     * @param string $word camelCasedString or PascalCasedString
     * @return string underscores_string
     */
    public static function camel2Underscores($word) {
        return preg_replace(
            '/(^|[a-z])([A-Z])/e',
            'strtolower(strlen("\\1") ? "\\1_\\2" : "\\2")',
            $word
        );
    }

    /**
     * convert underscores_string to PascalCasedString
     * @param string $word underscores_string
     * @return string PascalCasedString
     */
    public static function underscores2Pascal($word) {
        return preg_replace('/(^|_)([a-z])/e', 'strtoupper("\\2")', $word);
    }

    /**
     * convert underscores_string to camelCasedString
     * @param string $word underscores_string
     * @return string camelCasedString
     */
    public static function underscores2Camel($word) {
        return ucfirst(underscores2Pascal($word));
    }

    /**
     * convert camelCasedString to words string
     * @param string $word camelCasedString
     * @return string words string
     */
    public static function camel2Words($word) {
        return preg_replace(
            '/(^|[a-z])([A-Z])/e',
            'strlen("\\1") ? "\\1 \\2" : "\\2"',
            $word
        );
    }

    /**
     * convert camelCasedString to ucwords(words string) (Uppercase the first character of each word in a string)
     * @param string $word camelCasedString
     * @return string ucwords(words string)
     */
    public static function camel2Ucwords($word) {
        return ucwords(camel2Words($word));
    }

    /**
     * convert camelCasedString to ucfirst(words string) (a string's first character uppercase)
     * @param string $word camelCasedString
     * @return string ucfirst(words string)
     */
    public static function camel2Ucfirst($word) {
        return ucfirst(strtolower(camel2Words($word)));
    }

}