syntax-error

If I have a rich text box on a form, that is filled with say 30 lines of text the user has inserted. Is there a way I can detect where the cursor is in that text and insert some pre-defined text at its location on a button click? For example:

"This is some text in a rich text box. This is some text in a rich text box. This is some text in a rich text box. This is some text in a rich text box. This is some text in a rich text box. This is some text in a rich text box.<!!!!the cursor is here!!!> This is some text in a rich text box. This is some text in a rich text box. This is some text in a rich text box. This is some text in a rich text box."

How can I detect where the cursor is and insert some text at its location? Thanks.

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