<mesh-card id="card-123" hx-swap-oob="true">
    <template shadowrootmode="open">
      <link rel="stylesheet" href="/static/css/components/card.css" />
      <div class="card">
        <div class="card-header">
          <h3>Updated Card Title</h3>
        </div>
        <div class="card-content">
          Updated card description here.
        </div>
        <div class="actions">
          <button type="button">Edit</button>
        </div>
      </div>
    </template>
  </mesh-card>

  class MeshCard extends HTMLElement {
    connectedCallback() {
      if (!this.shadowRoot) {
        const tmpl = this.querySelector('template[shadowrootmode="open"]');
        if (tmpl) {
          this.attachShadow({mode: 'open'})
            .appendChild(tmpl.content.cloneNode(true));
        }
      }
    }
  }

  customElements.define('mesh-card', MeshCard);

The semver docs explicitly address this scenario. If a change in minor update breaks compatibility release a new minor update to revert the change.

Semver is just _indicative_ attempt at describing changes.

If this wasn't true, we wouldn't have lockfiles.

Ie. semver is just approximate attempt at change description that aids/helps development/maintenance but should never be fully trusted.

The only way it could fully work in automated fashion is if the whole program would be written in some formal proof language – then dependency upgrades could be considered as breaking or non breaking. But again, easier and more precise from end user position, not author's position because breaking change in one project can always be non breaking in other if that part is not used/used in more relaxed manner.

one great feature of htmx is how easy it is to understand and develop extensions for. I've just implemented this extension which allows safer handling of CSP nonce if this was required by an application. Hopefully this will get accepted as an official htmx extension.

My advice is if your not using inline script tags or the eval feature just keep it simple and disable allowScriptTags and allowEval and set a good CSP header. Also make sure you set a htmx-config meta tag in your page headers to set your config and protect from injected meta tags.

If you need inline scripts in a few places then be aware you need to choose a good templating or auto escaping engine on the backend to protect you and think about user inputs and be careful when using any raw escape override functions. If you have a sensitive application that needs regular external pen-testing then look at things like my safe-nonce extension that gives you another layer of protection to sell.

Loading malicious fragments: This is in no way related to htmx and is the same for all web implementations because you don't go get possible script code from random untrusted domains you don't trust or control. Also if he had tried this with the current version of htmx (2.0) he would have not been able to do this as it now defaults to blocking hx requests to external sites and you can only use local relative paths now. So win to htmx on this point.

Unsafe eval: Yeah unsafe eval looks bad but almost every other client side framework also has this same issue and it is very hard to turn this one off on any modern interactive or SPA like website today. Htmx has the option to just ignore the two features that need unsafe eval and implement these features with other more custom solutions unlike most other solutions so I have to chalk this up as a second win for htmx.

Disabling HTMX with hx-disable: I think it fair that hx-disable is not a fool proof security feature and is there to stop silly things and provide some isolation for content to separate it from htmx. But you should probably not allow un-sanitized data in here and expect this to save you.

Nonces for inline scripts: Yeah htmx has some support for nonces and they can protect from inline scripts inserted into the page somehow but they won't protect you from scripts returned from your trusted local server via hx requests by design. Another small win here.

Configuration meta tag: This one is a fair point and the use of malicious meta tags is an interesting attack vector. This may weaken some of the security features built into htmx but if you allow un-sanitized user input to be returned by your server like in his example app there are not many solutions that will come off any better off.

Conclusion: When a site uses HTMX, the attack surface of HTML injection is the same as any other SSR solution. It is possible to limit the risk of XSS by using a content security policy. Security is simple and old school as you just sanitize your inputs which all modern backend stacks now make easy. But it not possible to have all HTMX features and provide 100% security against injection (unless you sanitize all inputs and only link to your own server).