Some text of a text-box or text-area restrict to readonly

Hello Dear,

Thank you very much for seeing my post.

Would u pls let me know whether the following is possible or not:
User can be able to insert text on a text-box or text-area(form) as usually we use text-area to do so. But I want to put some readonly text using an open and close tag
for example:
<ro>This is readonly text</ro>insert your text here

Can I be able to make the text inside <ro>…</ro> tag readonly, it means user can’t be able to modify or delete this readonly text. readonly text length not fixed. only way to recognize the readonly text is the <ro> tag.

Thank you very much again,

I’ve done this before…

Admittedly can use some cleaning up, but that should put you down the right track.