string - Getting a substring of an attribute in XPATH -

given

<foo>   <bar baz="hello, world!"> </foo>

how last 4 characters of @baz? 1 of attempts was:

/foo/bar/@baz[substring( ., 0, -4 )]

use:

substring(/foo/bar/@baz, string-length(/foo/bar/@baz)-3)

do note 3 in expression.

the following wrong:

substring(/foo/bar/@baz, string-length(/foo/bar/@baz)-4)

because returns last 5 characters of string value of baz attribute.

shell