ey document what the variable is used for.<br />
<br />
Variable names can be arbitrarily long. They can contain
both letters and numbers, but they have to begin with a letter.
It is legal to use uppercase letters, but it is a good idea
to begin variable names with a lowercase letter (you'll
see why later).<br />
<br />
The underscore character (<code>_</code>) can appear in a name.
It is often used in names with multiple words, such as
<code>my_name</code> or <code>airspeed_of_unladen_swallow</code>.<br />