擅长:python、mysql、java
<p>从<a href="https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form" rel="nofollow noreferrer">wikipedia</a>:</p>
<blockquote>
<p>The "::=" means that the symbol on the left must be replaced with the expression on the right.</p>
</blockquote>
<p><code>|</code>符号表示独占的<code>OR</code>。你知道吗</p>
<p>这意味着你必须用<code>identifier</code>、<code>literal</code>或<code>enclosure</code>来替换<code>atom</code>。你知道吗</p>