 receive data on their sink pads and generate data on their source pads.</p><p>A pad can have three availabilities: always, sometimes, and on request.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>method</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lan