"Error in input" for parse errors isn't super helpful

[NicMcPhee]

Having the red "Error in input" message pop up when there's a parse error isn't terribly helpful.

We're using Instaparse for our parsing, and it does appear to provide fairly sophisticated info when a parse fails, so we presumably should be able to look at that info and try to highlight the error or provide some additional info that might help the user.