Various fixes 4

In preparing for the webinar this Wednesday I'm sure I'll run into some bugs.  Collecting them here.
No, the alternative is to answer the question: "What are all valid characters that might precede `sv` for foo-separated-value files".

I'm more concerned about false negatives than false positives here.  Happy to change this if you can think of a more restrictive class that won't have false negatives.  Perhaps `[a-zA-Z]`?  Hrm, we should probably support caps...