Thanks for reply.
I think you have not enough information about Arabic like languages.
In Arabic like languages (Arabic, Persian, Urdu,...) we have two type of letters.
Some of them are synthesis type letter like س، ل، ... and must join the next letter inside the word.
When we use <em> tag the word will break to two and it's wrong but with span tag we will get correct view of words.
Please check attached htm file as a simple sample.