net symbols are represented as a sequence of alphanumeric characters not
starting with a digit or a colon. They can also contain the characters <code class="mendoza-code">!</code>,
<code class="mendoza-code">@</code>, <code class="mendoza-code">$</code>, <code class="mendoza-code">%</code>, <code class="mendoza-code">^</code>, <code class="mendoza-code">&amp;</code>, <code class="mendoza-code">*</code>, <code class="mendoza-code">-</code>, <code class="mendoza-code">_</code>,
<code class="mendoza-code">+</c