How to do struct validation for slice of strings

[dancb10]

Hello,
I have tried validating struct element which is slice of strings. I've tried using the following functions but somehow they don't work as expected:
"range(min|max)": Range,
"length(min|max)": ByteLength,
"runelength(min|max)": RuneLength,
"stringlength(min|max)": StringLength,

How can you say my slice cannot have more than 5 elements and each element cannot be more than 20 alpha characters?
Can you do this with the validator and using struct tags?