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Check for UTF-8

<?php
/**
 * Returns true if $string is valid UTF-8 and false otherwise.
 *
 */
function is_utf8 ($string) {
	// From http://w3.org/International/questions/qa-forms-utf-8.html
	return preg_match (
		'%^(?:
              [x09x0Ax0Dx20-x7E]            # ASCII
            | [xC2-xDF][x80-xBF]             # non-overlong 2-byte
            |  xE0[xA0-xBF][x80-xBF]        # excluding overlongs
            | [xE1-xECxEExEF][x80-xBF]{2}  # straight 3-byte
            |  xED[x80-x9F][x80-xBF]        # excluding surrogates
            |  xF0[x90-xBF][x80-xBF]{2}     # planes 1-3
            | [xF1-xF3][x80-xBF]{3}          # planes 4-15
            |  xF4[x80-x8F][x80-xBF]{2}     # plane 16
        )+z%xs', $string);
}
?>

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Returns true if $string is valid UTF-8 and false otherwise.