Do here-strings undergo word-splitting?

Quoting Bash Reference Manual and man bash (version 4.3):

[n]<<< word

The word undergoes brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal. Pathname expansion and word splitting are not performed.

The word should not undergo word-splitting. However, using this simple code:

var="a    b"

cat <<< $var
#output:
#a b

cat <<< "$var"
#output:
#a    b

What am I missing? Does this depend on the version of bash or is there a mistake in the manual? I am using GNU bash, version 4.3.48.

Answer

The change from splitting here-strings to not splitting them happened between bash-4.4-alpha and bash-4.4-beta. Quoting from CHANGES:

Bash no longer splits the expansion of here-strings, as the documentation has always said.

So the manuals of older Bash versions mentioned it, but didn’t actually do it.