Improve frontend guidelines (#23007)

Some were out-dated, some are added.

docs/content/doc/developers/guidelines-frontend.en-us.md

@@ -39,12 +39,20 @@ We recommend [Google HTML/CSS Style Guide](https://google.github.io/styleguide/h
 ### Gitea specific guidelines:
 
 1. Every feature (Fomantic-UI/jQuery module) should be put in separate files/directories.
-2. HTML ids and classes should use kebab-case.
+2. HTML ids and classes should use kebab-case, it's preferred to contain 2-3 feature related keywords.
 3. HTML ids and classes used in JavaScript should be unique for the whole project, and should contain 2-3 feature related keywords. We recommend to use the `js-` prefix for classes that are only used in JavaScript.
-4. jQuery events across different features could use their own namespaces if there are potential conflicts.
-5. CSS styling for classes provided by frameworks should not be overwritten. Always use new class-names with 2-3 feature related keywords to overwrite framework styles.
-6. The backend can pass complex data to the frontend by using `ctx.PageData["myModuleData"] = map[]{}`
-7. Simple pages and SEO-related pages use Go HTML Template render to generate static Fomantic-UI HTML output. Complex pages can use Vue3.
+4. CSS styling for classes provided by frameworks should not be overwritten. Always use new class names with 2-3 feature related keywords to overwrite framework styles. Gitea's helper CSS classes in `helpers.less` could be helpful.
+5. The backend can pass complex data to the frontend by using `ctx.PageData["myModuleData"] = map[]{}`, but do not expose whole models to the frontend to avoid leaking sensitive data.
+6. Simple pages and SEO-related pages use Go HTML Template render to generate static Fomantic-UI HTML output. Complex pages can use Vue3.
+7. Clarify variable types, prefer `elem.disabled = true` instead of `elem.setAttribute('disabled', 'anything')`, prefer `$el.prop('checked', var === 'yes')` instead of `$el.prop('checked', var)`.
+8. Use semantic elements, prefer `<button class="ui button">` instead of `<div class="ui button">`.
+9. Avoid unnecessary `!important` in CSS, add comments to explain why it's necessary if it can't be avoided.
+
+### Accessibility / ARIA
+
+In history, Gitea heavily uses Fomantic UI which is not an accessibility-friendly framework.
+Gitea uses some patches to make Fomantic UI more accessible (see the `aria.js` and `aria.md`),
+but there are still many problems which need a lot of work and time to fix.
 
 ### Framework Usage
 

web_src/js/features/aria.md

@@ -1,5 +1,32 @@
 **This document is used as aria/a11y reference for future developers**
 
+# Checkbox
+
+## Accessibility-friendly Checkbox
+
+The ideal checkboxes should be:
+
+```html
+<label><input type="checkbox"> ... </label>
+```
+
+However, related styles aren't supported (not implemented) yet, so at the moment, almost all the checkboxes are still using Fomantic UI checkbox.
+
+## Fomantic UI Checkbox
+
+```html
+<div class="ui checkbox">
+  <input type="checkbox"> <!-- class "hidden" will be added by $.checkbox() -->
+  <label>...</label>
+</div>
+```
+
+Then the JS `$.checkbox()` should be called to make it work with keyboard and label-clicking, then it works like the ideal checkboxes.
+
+There is still a problem: Fomantic UI checkbox is not friendly to screen readers, so we add IDs to all the Fomantic UI checkboxes automatically by JS.
+
+# Dropdown
+
 ## ARIA Dropdown
 
 There are different solutions:
@@ -27,7 +54,7 @@ At the moment, `menu + menuitem` seems to work better with Fomantic UI Dropdown,
 <div class="ui dropdown"> <!-- focused here, then it's not perfect to use aria-activedescendant to point to the menu item -->
   <input type="hidden" ...>
   <div class="text">Default</div>
-  <div class="menu transition hidden" tabindex="-1">
+  <div class="menu" tabindex="-1"> <!-- "transition hidden|visible" classes will be added by $.dropdown() and when the dropdown is working -->
     <div class="item active selected">Default</div>
     <div class="item">...</div>
   </div>
@@ -38,7 +65,7 @@ At the moment, `menu + menuitem` seems to work better with Fomantic UI Dropdown,
   <input type="hidden" ...>
   <input class="search" autocomplete="off" tabindex="0"> <!-- focused here -->
   <div class="text"></div>
-  <div class="menu transition visible" tabindex="-1">
+  <div class="menu" tabindex="-1"> <!-- "transition hidden|visible" classes will be added by $.dropdown() and when the dropdown is working -->
     <div class="item selected">...</div>
     <div class="item">...</div>
   </div>