# This "good first bug" is taken by @YongPilMoon. Don't work on it unless that's you!

This has been discussed a few times before but I don’t think there was any conclusion, and PRs intending to solve the issue were not merged for various reasons.

I would like to close those PRs as outdated, and reboot the discussion about this.
Performance considered, the conclusion from @sebmarkbage and @syranide seems to be:

> We should consider not allowing conflicting style rules at all.

— https://github.com/facebook/react/pull/2013#issuecomment-57338177

> IMHO, all things considered it's better to just disallow overlapping and warn in dev.

— https://github.com/facebook/react/pull/4661#issuecomment-132996649

Radium by @ianobermiller came to the same conclusion in https://github.com/FormidableLabs/radium/issues/95 but there was some backlash afterwards. React Native seems to allow style expansions but only for a few attributes (e.g. `margin` and `padding`, but not `border`).

I’m closing old pull requests about this, and creating this issue to track implementation of the behavior we seem to agree upon: we should warn in `__DEV__` when `border` and `borderBottom` are used at the same time. We can discuss more specifics (should either be ignored? should we allow a few whitelisted properties but warn for others?) in this issue.

As a migration strategy, we can suggest people to use something like https://github.com/ActionIQ/style-builder if they really need those shortcuts. It’s also something we’ll need to decide upon when implementing integrated styling.

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Related issues:
- #2231
- #2407
- #5030
- https://github.com/FormidableLabs/radium/issues/95

Related PRs:
- #2013
- #4661

ReactDOM.render(
        <svg>
          <image
            xlinkHref="http:example.org/image"
            onError={e => console.log('onError called')}
            onLoad={e => console.log('onLoad called')}
          />
        </svg>,
        container,
      );
      const loadEvent = document.createEvent('Event');
      const errorEvent = document.createEvent('Event');
      loadEvent.initEvent('load', false, false);
      errorEvent.initEvent('error', false, false);
      container.getElementsByTagName('image')[0].dispatchEvent(errorEvent);
      container.getElementsByTagName('image')[0].dispatchEvent(loadEvent);
      if (__DEV__) {
        expect(console.log).toHaveBeenCalledTimes(2);
        expect(console.log.calls.argsFor(0)[0]).toContain('onError called');
        expect(console.log.calls.argsFor(1)[0]).toContain('onLoad called');
      }
    });
    it('should receive a load event on <link> elements', () => {
      const container = document.createElement('div');
      const onLoad = jest.fn();
      ReactDOM.render(
        <link href="http:example.org/link" onLoad={onLoad} />,
        container,
      );
      const loadEvent = document.createEvent('Event');