code: static function FindStartTagByPrefix(&$Txt, $TagPrefix, $PosBeg, $Forward=true) {
  
  		$x = '<'.$TagPrefix;
  		$xl = strlen($x);
  
  		if ($Forward) {
  			$PosBeg = strpos($Txt, $x, $PosBeg);
  		} else {
  			$PosBeg = strrpos(substr($Txt, 0, $PosBeg+2), $x);
  		}
  		if ($PosBeg===false) return false;
  
  		// Read the actual tag name
  		$Tag = $TagPrefix;
  		$p = $PosBeg + $xl;
  		do {
  			$z = substr($Txt,$p,1);
  			if ( ($z!==' ') && ($z!=="\r") && ($z!=="\n") && ($z!=='>') && ($z!=='/') ) {
  				$Tag .= $z;
  				$p++;
  			} else {
  				$p = false;
  			}
  		} while ($p!==false);
  
  		return new clsTbsXmlLoc($Txt, $Tag, $PosBeg);
  
  	}
docs: Search a start tag by the prefix of the element