Flex 4 textFlow how using tags h1, i and etc.

If you are passing the html importer a string it uses a fairly slow process to make XML out of it.  It can't call XML(string) because it needs to handle street html like TextField does.

Before calling the importer do this (source is your string):

            var originalSettings:Object = XML.settings();
            try
            {
                XML.ignoreProcessingInstructions = false;       
                XML.ignoreWhitespace = false;
                var xmlSource:XML = new XML(source);               
            }           
            finally
            {
                XML.setSettings(originalSettings);
            }

And pass xmlSource to the importer.

Hope that helps,

Richard