Presumably, if the terminator is prefixed with 1 or more tabs, then that same number of tabs will be removed from the other lines (if they are present), and if it has 2 spaces and a tab, the 2 spaces and a tab will be removed from the other lines if present?
This won't do the right thing if the whitespace is mixed and variable, but it might do 'the right thing' more often than not.
From what I've read around the Monastery, you'd be forgiven that HEREDOCS were dangerous, unuseful animals that should have been depricated long ago.
It's nice to see an old favorite of mine reinventing itself. I wonder if this change will satisfy its detractors?