ts, variables, object properties, and other expressions. These can
be used to express invariants in your program and catch problems due to input errors,
incorrect function usage, or other bugs.
</p>
<p>These validation functions are named following the pattern <code class="code">mustBeXxx</code>, where <code class="code">Xxx</code>
is some property of the input it is testing. Validation functions may check the type,
size, or other aspects of their inputs.
</p>
<p>The most common place for validation functio