# Sometimes \w matches U+E9.
$ perl -Mfeature=say -e'say "\xE9" =~ /^\w/ || 0'
0

# Sometimes it doesn't.
$ perl -Mfeature=say -e'say "\xE9\x{2660}" =~ /^\w/ || 0'
1

# \w always matches U+E9 with "use 5.014;".
$ perl -Mfeature=say -e'use 5.014; say "\xE9" =~ /^\w/ || 0'
1

# \p{Word} always matches U+E9, period.
$ perl -Mfeature=say -e'say "\xE9" =~ /^\p{Word}/ || 0'
1