Thank you for your post!
FileMaker Server 13 isn't tested working on El Capitan (I know most run into some trouble with it). I would not expect FileMaker Server 12 to run reliably on OS X El Capitan. You might see System Requirements for FileMaker Server 12 and FileMaker Server 12 Advanced.
I hope this helps!
Thanks, TSPigeon! Yes, I knew the System Requirements as far as 12 not being *tested* with El Capitan - heard some reports that it worked OK, though, and wanted to ask the community.
On a related note, per my mention of IWP vs. WebDirect: do you know of any documentation/resources that walk users through the transition and implementation? Thank you!
I understand completely. I hope you receive some further advice on Server 12's usability on El Capitan.
You can find the main differences between the two technologies in Knowledge Base Article #12506. There isn't a specific article to explain the transition from Instant Web Publishing to WebDirect. For more information you might check out the FileMaker 15 WebDirect Guide.