Bug with encoding hex characters with letters

[Fabimawn]

The line: local testStr = jsonLua.encode("\x03test\x7a")
Outputs: "\u0003testz"

The first HEX charater is converted correctly, the second one isn't. If I make the second one a HEX only consisting of a number it converts correctly.
It doesn't matter if you use upper or lower case, alphanumerics in the HEX character doesn't seem to work.

[Fabimawn]

It seems to work up to 1F. Is it only escaping control characters? Probably design choice then.