TextExpander in Yosemite is giving an odd TextExpander Helper warning, what do I do? (Mac)

Yosemite may repeatedly alert you that “TextExpander Helper would like to control this computer using accessibility features”. Clicking “Open System Preferences” may show TextExpander already in the list and checked. It is confusing because:
– The message refers to TextExpander Helper, which handles some functions for TextExpander, and needs separate permission, and,
– OS X Yosemite 10.10 and 10.10.1 sometimes refuses to display TextExpander Helper in that list of Accessibility permissions. (This may be fixed in OS X 10.10.2)

You can find an explanation and solution in our blog post “Yosemite, TextExpander Helper, and Accessibility Permission”.