Wrapround a Selection area with <span> tag

Hi,

I have a requirement, where I need to wraparound a selected area with span tag and apply some style sheet. now the selected tag can also have some html tag. so all those tags should remain as it is. It means whatever selection I do, it should be start with span tag and end with span tag.

Please help me out in this.

Thanks in advance

Regards,
Roshan Salvi