IEEE 830-1998 says: “SRS (software requirements specification) should be correct, unambiguous, complete, consistent, ranked for importance and/or stability, verifiable, modifiable, traceable”.
As a controlled natural language (CNL) Requs enables the creation of such documents in plain text format. Requs resembles English but has a very strict syntax and semantic.
Try online demo: demo.requs.org.
Check also this blog post: Incremental Requirements With Requs. It explains how Requs is used in XDSD projects by Zerocracy.