Block theme templates are files, and this edits the files

By looking at your theme, and only at your theme. A block theme is one whose own directory carries both a theme.json and a templates/ folder. The naive check — is any installed theme a block theme — is true on very nearly every WordPress in existence, because core has shipped three block themes in the default download for years, so a site running a hand-written classic PHP theme would be misread as Full Site Editing. PortBay strikes out core's bundled twenty-something themes as evidence about core rather than about your site, and if exactly one theme survives that, that is your theme. If nothing survives or several do, it answers classic on purpose: a wrong classic guess costs you one sentence, and a wrong block guess would refuse the only editing tier a classic theme has.

The theme's own block templates and template parts — templates/index.html, parts/header.html and their neighbours. Those are ordinary files with block markup in them, so text, class and attribute edits resolve into them and write back with your formatting intact. The cross-stack parity test drives all three lanes against a real block-theme fixture at wp-content/themes/acme/templates/index.html and each one writes. What is not on that list is page content and page settings, and the next two answers are about why.

Because they are not in your repository. On a Full Site Editing site, a page's content is serialised block markup stored in a database row, so a text search of your theme finds it in neither the source nor the templates. That is the defining difference from a classic theme, where the markup is usually sitting in a PHP file that PortBay can search. Rather than fall back to the nearest similar-looking text somewhere in the theme — which on a WordPress site can genuinely find the same words in a place the page did not get them from — PortBay tells you what it hit.

No, and this is the one place in the whole product where a lane refuses outright. Across twenty-one stacks and four write lanes, PortBay's own parity test records exactly two refusals, and both are WordPress page settings, both carrying the same message: it cannot connect to this site's database. A WordPress page's title and its SEO fields are wp_posts and wp_postmeta rows, so there is no file to write. If a page on this site ever tells you otherwise, it is wrong.

No, because PortBay refuses the change that would. A stock FSE template is a file; it only becomes a database row when somebody customises it in the site editor, and from then on the row wins forever — theme updates to that template stop reaching the site and the editor starts offering a Reset button. Writing that row on your behalf would be a durable change to how your site is maintained, made as a side effect of editing one word, and creating it correctly means getting rows right across four tables. The undo would be a delete, and nothing in PortBay deletes. So it refuses by name, names the file, and points you at the two paths that work: edit the theme file, or customise the template once in the site editor and let WordPress create the row it knows how to create.

No. theme.json is how PortBay recognises your theme as a block theme, not somewhere it writes. A block theme's fonts belong under settings.typography.fontFamilies in that file — the site editor reads them from there, and a stylesheet PortBay wrote instead would be invisible to it, which is worse than doing nothing. PortBay has no theme.json writer, and it says so rather than putting the declaration somewhere that renders but does not show up in the editor you will open next.

PortBay's visual editor is a Pro feature, in early access behind an opt-in toggle in Settings, and it is not compiled into the open-source build at all. It attaches to local .test hosts only and refuses while a project is shared over a public tunnel — the edit bar never applies to tunneled traffic, so you stop the share first. It is one live page at one breakpoint at a time rather than a multi-frame infinite canvas. Running WordPress locally — PHP, the database, the hostname, trusted HTTPS, the task board — is all in the free, open-source app.