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var bits:Array = new Array();

function addHtmlTag(tf:MovieClip,indexStart:Number,indexEnd:Number,tag:String):String{
bits = new Array();
bits = getStringParts(tf,indexStart,indexEnd);
if(bits != undefined){
var newString:String = bits[0] + " <" + tag + ">" + bits[1] + " </" + tag + ">" + bits[2];
return newString;
}
}

function getStringParts(tf:MovieClip,indexStart:Number,indexEnd:Number):Array{
var wholeString:String = tf.htmlText;
var totalIndex:Number = wholeString.length;
bits.push(wholeString.substring(0,indexStart));
bits.push(wholeString.substring(indexStart,indexEnd));
bits.push(wholeString.substring(indexEnd,totalIndex));
//trace("bits: "+bits);
return bits;
}

// usage
// var newText:String = addHtmlTag(myTextField_mc, 0, 10, "b");

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