I have a textbox where I accept multiple email ids separated by a comma. I then split it in my code-behind. If an email id is invalid, I change the background of it using Regex.replace, like this:
Regex.Replace(InputTxt, Search_Str, StartTag & "$1" & EndTag, RegexOptions.IgnoreCase)
My start and end tags are definned as:"<Span class=highlight>" and "</span>"
Go to the complete details ...