Click a Rails view, change the .html.erb that rendered it

No, and that is the main confusion worth clearing up. Froala, TinyMCE and the rest of that category are WYSIWYG fields you embed in your app so that end users can write content, which is then stored in your database. This is a developer tool: it edits the .html.erb templates in your repository, and the change shows up in git.

One line in the :development group of your Gemfile, then a restart. The gem ships a Railtie, and Rails loads a Railtie for every gem in the Gemfile, so it registers the ERB template handler itself. There is no initializer to paste, no config/application.rb edit, and no TEMPLATES-style configuration to maintain. It requires Ruby 3.1 or newer and ActionView and Railties 7.0 or newer.

Yes — that is the part worth checking, because it is where naive approaches break. Each template is stamped in its own source, so an element in a partial points at the partial, and an element in a content_for block that renders through the layout's yield points at the block, not the layout. On served HTML measured against a zero-stamp control, 18 of 18 coordinates were exact on both Rails 8.1.3.1 and 7.2.3, covering the layout, a page view, a rendered partial, a content_for block, and a three-row collection render.

Yes. A Turbo Frame response is markup the server rendered through the same stamped templates, so the coordinates arrive with it — a Turbo Frame response measured 3 of 3 exact in the same run. That is a real difference from stacks that swap in markup assembled on the client, where the server never saw the fragment.

Elements built with tag or content_tag carry no coordinate, because there is no source tag in your template to stamp. An element written as <h1 class="hero"> gets a stamp; the same element written as tag.h1 does not. Those still edit — PortBay resolves them by searching your source files and refuses rather than guessing when the match is ambiguous — but you lose the exactness the stamper gives you elsewhere. Only .html.erb is stamped; .text.erb, .json.erb, .js.erb and .xml.erb are never touched.

No. The stamp is applied to the template source in memory, on its way through ActionView's ERB handler — the file on disk is never opened for writing, so no data-pb-loc and no marker attribute ever reaches your repository. When you save an edit, PortBay splices only the bytes that changed: a one-class change shows up in git diff as one changed token, and a multi-line attribute keeps its indentation.

No. It is a Pro feature, still in early access behind an opt-in toggle in Settings, and it is not compiled into the open-source build. It is also unavailable on a project while that project is publicly tunneled — the edit bar and its write-back endpoints are never routed onto public traffic. Running the Rails app, the database, the .test hostname and trusted HTTPS are all in the free, open-source app.