Not a rumor. A friend was on the WP team and told me that assembler was heavily used.

WP was fast, but my three biggest gripes were

- the required keyboard template. Lose that, you were lost.
- Esc Esc for help. Stupid combination and totally didn't make sense
- Impossible to edit an existing document without Reveal Codes. WordStar, for example, was smarter in that respect.

>- WordPerfect for DOS: amazingly fast even on slow hardware. The rumour I heard was significant parts were written in x86 assembler