Initially I had the same response as Daniel Jalkut, namely that you should have checked the license and either not used the code, or complied with its terms.
However, I also note the following:
- WordPress-iOS-Editor uses a lot of BSD and MIT licensed code.
- The license and attribution appears to have gone missing from some of that code — WPEditorView.m, in particular, seems to be based on ZSSRichTextEditor.m, but is missing any copyright notice or acknowledgement.
- You cannot, without the authors’ permission, re-license BSD or MIT code as (L)GPL. BSD and MIT licensed code is compatible with GPL and can be used in GPL’d projects; it is possible to have dual-licensed files (where some of the code is covered by a BSD or MIT license and the rest by GPL), but that doesn’t mean that the BSD or MIT licensed code magically becomes itself subject to the GPL — it does not. The LICENSE file at the top level of WordPress-iOS-Editor is therefore rather misleading — it should really contain copies of the licenses for ZSSRichTextEditor, CYRTextView, HRColorPicker, JQuery and JS Beautifier as well as the GPL.
- (L)GPL is in any event completely incompatible with iOS development. You cannot use LGPL or GPL’d code in an iOS app. It is impossible to have a GPL’d iOS app, at least in the App Store. Why? Because in order to build it, you must be a member of Apple’s Developer Program, and the terms and conditions for that program are not compatible with the GPL. Even in the case of LGPL, the resulting binary will breach the requirement that end users can re-link your application with different versions of the LGPL covered code.
So I will revise my original statement: Wix is in the wrong here, because it should not have used the code. It is impossible to use WordPress-iOS-Editor in any iOS app, because you cannot comply with the license—it’s incompatible with the terms of the Apple Developer Program. But WordPress is also in the wrong, firstly for releasing “Open Source” code that nobody can actually use (using it is a breach of its license), and second for not properly acknowledging some of the (non-GPL’d) code in the project.