How to read someone else's code to reap the most?

How to see people's code to receive the most? What are the high-quality PHP classic open source code? There is a certain basis, how to improve their ability?

Reply to discussion (solution)

Different traits.
A lot of people will find their own class to learn, I feel very headache to this
I read more about other people's Questions and answers, stackoverflow.com and this is my resource pool.

Different traits.
A lot of people will find their own class to learn, I feel very headache to this
I read more about other people's Questions and answers, stackoverflow.com and this is my resource pool.
Oh, stackoverflow.com this site is really good.

In fact, research on the CMS is also very good, like Joomla, Drupal, WordPress, etc. are quite excellent.

Dedecms thought very well, especially the table structure

