Since appr. 1 year, under MacOS 10.10/10.11/10.12, anchor links in a WebViewer won't work anymore. There is no problem with the same links under windows, iOS, or WebDirect. Under MacOS, in Filemaker 13 nothing happens when I click an anchor link. In Filemaker 15, there comes an alert (see appendix). Following the advice of the alert, it is not possible to choose Filemaker or any other program to open the link.
Tested on several machines and several Versions of MacOS and several kinds of HTML code.