validation for substr(path/to/node, start, end) fails if end parameter is provided

[MartijnR]

Not sure if ODK validate or pyxform issue.

[MartijnR]

same if ${thing} syntax is used

[nathanathan]

It's an ODK Validate problem. It's on the ODK issue tracker here: https://code.google.com/p/opendatakit/issues/detail?id=832&start=200

Although, once the fix is added to Collect and Validate the Validate jar in XLSForm will need to be updated, so let's leave the issue open here until that happens.