Treats list as a list and returns a decimal string giving the number of elements in it.
The result is the number of elements:
% llength {a b c d e}
5
% llength {a b c}
3
% llength {}
0
Elements are not guaranteed to be exactly words in a dictionary sense of course, especially when quoting is used:
% llength {a b {c d} e}
4
% llength {a b { } c d e}
6
An empty list is not necessarily an empty string:
% set var { }; puts "[string length $var],[llength $var]"
1,0