[davidperel]

We didn't want to fork WordPress and turn it into a Frankenstein. The actual core of WP is untouched however if you look at our code and the interface, we've tried to stick as close to what WP recommends as possible.

Many existing WP page builders out there look nothing like WordPress at all. Their interfaces are totally different and their code is not to WP's high standards. We wanted to avoid that with Layers. We wanted you to still use WP as is without feeling like you'd just installed something that takes over the normal experience.

[mikeschinkel]

Further commentary, you could also instead say "Built with a look and feel that would make you think it is built into WordPress core." But not "Built into WordPress core."