There are many instances where we list CDH version numbers and corresponding Impala version numbers right next to each other, e.g. "In CDH 5.5 / Impala 2.3 and higher, you can use such-and-such a feature". Probably we will set up a substitution variable so that in the ASF docs these references can resolve to just the Impala version number, while in vendor-specific docs it can be changed to the right naming/numbering for that vendor if they republish the same content.
There are also some contexts where space is at a premium, e.g. in headings, where we only reference the CDH version number. For example, "FOO Data Type (CDH 5.5 or higher only)". These could be handled by a second substitution variable, or perhaps folded into the first substitution variable if it was appropriate for vendor-specific docs to avoid repeating Impala version numbers all over the place.