TextFX is open source and every example has a "look behind the scenes" button that shows the prompt, which is broken down into a preamble and then a set of examples:
For instance, their prompt for the acronym generator is:
An acronym is an abbreviation of several words in such a way that the abbreviation itself forms a pronounceable word.
Here is an acronym that uses the letters of the word "rap": RAP - Recognizing Analogous Patterns
Here is an acronym that uses the letters of the word "mural": MURAL - Magnifying Urban Realities Affecting Lives
[continued]
Here is an acronym that uses the letters of the word "":
They then do postprocessing to check that the completion matches the expected format.