(?!\w) and (?=\W)

and also

(?<=\w) and (?<!\W)

are equivalent!?

This would unify your "descripted" \b and japhy's "left side boundary".

Also, if it ... flies like a duck, quacks like a duck. .. It probably is a duck?!:

Do I have the wrong test cases?

(?!\w) and (?=\W) differ at the end of the string.

(?<=\w) and (?<!\W) differ at the start of the string.

Oh, I was vaguely aware of it. But I didn't realize that that was the exact point japhy addressed!

Read more... (911 Bytes)

[\b                             ]*this*,
[(?:(?=\w)(?<!\w)|(?=\W)(?<!\W))]*this*,
[(?:(?<=\w)(?!\w)|(?<=\W)(?!\W))]this*,*
[(?(?=\w)(?<!\w)|(?<!\W))       ]*this*,
[(?(?<=\w)(?!\w)|(?!\W))        ]*this*,*
[(?:(?=\w)(?<!\w)|(?!\w)(?<=\w))]*this*,
[\b                             ],*that*
[(?:(?=\w)(?<!\w)|(?=\W)(?<!\W))]*,*that
[(?:(?<=\w)(?!\w)|(?<=\W)(?!\W))],*that*
[(?(?=\w)(?<!\w)|(?<!\W))       ]*,*that*
[(?(?<=\w)(?!\w)|(?!\W))        ],*that*
[(?:(?=\w)(?<!\w)|(?!\w)(?<=\w))],*that*
[download]