The Rules are design by the Magento Commerce. So if you follow the below rules then it will help to developing a magento Application.
- Rule 1: Do NOT edit the files in the base package
- Rule 2: Do not create a custom theme inside of the base package
- Rule 3: Create your customized themes inside of their own design package. Make directories atapp/design/frontend/your_custom_package/default andskin/frontend/your_custom_package/default and build your custom theme there.
- Rule 4: Do not copy all the files from base/default into your custom package. Copy only the files that you modify.
- Rule 5: Do not create your custom theme inside of the default/default directories, even though there are old instructions that may tell you to do so. This approach was never recommended.
- Rule 6: Do not copy all the files from default/default into your custom package as a starting point, even though there are old instructions that may tell you to do so. This approach has been deprecated.
- Exception to Rule 6: Because base/default does not contain full CSS files, you may want to copy the CSS from one of the demo themes into your new custom themes as a starting point. Many designers and developers prefer to start with nothing and build their CSS from scratch though, so you can do this too. In general, if you do copy over CSS and image files to your new custom package, the blank theme (default/blank) provides the leanest CSS.
- 2nd Exception to Rule 6: Enterprise customers for now DO need to copy the files from enterprise/default into their custom package as a starting point. In a future release, the Enterprise files will be folded into the base/default directories but they are not in EEv1.8.
- Rule 7: Break the rules if you have to, just do so knowingly.
All rules are taken from the