Because it might be useful to have conditional text possibilities in Drupal, I'll try to describe such a scenario; possibly inspiring others. Given time I might develop a conditional text module myself, but it will take a while, as there's still a few skills I need to acquire.
Text might be made conditional to documents intended for different audiences or media. Imagine you were writing general documentation about Drupal, and needed to discuss Drupal forms. There's quite a difference in the way forms are handled between versions prior to v 4.7 and subsequent versions. So two books are required, but tracking changes manually between the two different books is error-prone, time-consuming, and laborious.
Imagine conditional text working in a Drupal environment as follows:
Most of the text is common to both documents, and remains unaltered.
Text conditional to v4.7 is selected (somehow, not very relevant, lots of possibilities) and high-lighted with a pleasant green tint. Similarly text unique to v4.6 is high-lighted as a pleasant red.
Near Preview / Submit are check-boxes labelled 'v4.7' and 'v.4.6'; Each box include/excludes the conditional version from rendering upon Preview/ Submit.
Another checkbox toggles the colored high-lighting on or off, at render-time.
In terms of mark-up, the selections are simple spans, supported by a style-sheet.