refStringNewLen
Creates a new reference counted string and copies the contents of @str into it, up to @len bytes.
Since this function does not stop at nul bytes, it is the caller's responsibility to ensure that @str has at least @len addressable bytes.
Return
the newly created reference counted string
Since
2.58
Parameters
str
a string
len
length of @str to use, or -1 if @str is nul-terminated