Twitter community adds a context note to Joe Biden tweet:  The official Twitter account for the president tweeted, “Do you know what American billionaires pay on average in taxes? 8 percent. No billionaire should pay a lower tax than a teacher or firefighter. I’m calling on Congress to pass my proposal for a billionaire minimum tax.” Twitter added a label to the post that read "Readers added context they thought people might want to know.” The added context read "Biden’s 8% tax statement comes from a theoretical calculation that would include unrealized capital gains (increase in the value of unsold stocks) as income even though it isn't taxable under existing federal law. (Taxes legally occur when stocks are sold for profit.) " The context note also included several links that supported the note. The label is part of Twitter’s Community Notes system. Twitter users are able to sign up as contributors to add context to tweets.