# 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I would like to close those PRs as outdated, and reboot the discussion about this.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.

---

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

Related PRs:
- #2013
- #4661

expect(stubStyle.display).toEqual('');
      expect(stubStyle.color).toEqual('');
    });
    it('should update styles when `style` changes from null to object', () => {
      const container = document.createElement('div');
      const styles = {color: 'red'};
      ReactDOM.render(<div style={styles} />, container);
      ReactDOM.render(<div />, container);
      ReactDOM.render(<div style={styles} />, container);
      const stubStyle = container.firstChild.style;
      expect(stubStyle.color).toEqual('red');
    });
    it('should not reset innerHTML for when children is null', () => {
      const container = document.createElement('div');
      ReactDOM.render(<div />, container);
      container.firstChild.innerHTML = 'bonjour';
      expect(container.firstChild.innerHTML).toEqual('bonjour');
      ReactDOM.render(<div />, container);
      expect(container.firstChild.innerHTML).toEqual('bonjour');
    });
    it('should reset innerHTML when switching from a direct text child to an empty child', () => {
      const transitionToValues = [null, undefined, false];
      transitionToValues.forEach(transitionToValue => {
        const container = document.createElement('div');
        ReactDOM.render(<div>bonjour</div>, container);
        expect(container.firstChild.innerHTML).toEqual('bonjour');
        ReactDOM.render(<div>{transitionToValue}</div>, container);
        expect(container.firstChild.innerHTML).toEqual('');
      });
    });