If a string (and the mainframe does not process striings) is highlighted, it is already displayed. . .
What you want to do needs clarification.
From the line of questions, i suggest you learn what a "3270" can do and design/code within those capabilities.
If you want a "Windows" presentation, suggest you write the presentation code in other than "3270". If this is not already being done in your organization, it may be quite difficult to convince management to move in this direction. . .