autocommit commented out -- what is the default?

[Brian Whitman]

Hi, if you comment out the block in solrconfig.xml

<!--
   <autoCommit>
      <maxDocs>10000</maxDocs>
      <maxTime>600000</maxTime>
    </autoCommit>
-->

Does this mean that (a) commits never happen automatically or (b) some
default autocommit is applied?