HTML/CSS content
HTML/CSS/PHP UI content is confined to the project's ui/ directory. .html and
.css entries are structurally validated. Inline <script> lifecycle
objects use the sandboxed JavaScript API. CSS-only entries are valid content behaviors
with no callbacks. HTML and inline scripts have no DOM, network, filesystem, or Node
APIs. Web entries participate in gameplay lifecycle and state updates; they never
render or replace the editor shell.