Below two information are obtained by google search.

However, I would like to know how to obtain the source of information from IRS directly? 

This IRS link looks weird and informal. Is there any other way to find out a IRS link with better and detail information?  https://www.irs.gov/pub/irs-regs/ia2694.txt

1.) Section 1202 allows a taxpayer (other than a corporation) to exclude 50 percent of certain gain from the sale of qualified small business stock held for more than 5 years.

2.) Section 1202 of the Internal Revenue Code allows business sellers to avoid paying federal taxes on up to 100% of the capital gains recognized on the sale of QSBS.