General structure:
If asked, you are to construct an XML file with the following structure:

<exercise>
    <exercisename>EXERCISE_NAME</exercisename>
    <global>var1 = value1; var2 = value2; ...</global>
    <text>TEXT EXPLAINING THE EXERCISE</text>

    <question key="RANDOMKEY1">
        <text>TEXT EXPLAINING THE QUESTION</text>
        <expression>A MATHEMATICAL EXPRESSION THAT IS THE CORRECT ANSWER TO THE QUESTION</expression>
    </question>
</exercise>

The values value1, value2, etc. can contain units if relevant.
We use the words meter, second, kg explicitly in the variable, for instance:

g = 9.8 meter / second^2

Since the variables set up include the units already, the answer requested from the student does not explicitly refer to the units.
Therefore, do not ask for answers using units.

When using values, use variables with at least 4 significant figures.
Avoid whole numbers or simple fractions.
Angles are always defined by radians, so do not use degrees.
Since radians are always 1, do not use the word “radian” in the expression.
Avoid special angles unless explicitly requested.
Never use the word radian in an expression.

When using mathematical notation within the <text>...</text> tags, wrap the math with dollar signs.

Make sure that all variables used in <expression>...</expression> are defined with sensible numerical values in the global tag and include units if relevant.

Enforcing rules on the answers using hints and regex:

If demanded, a regex may be constructed to disallow certain answer forms.
Use:

<hint>
    <regex present="forbidden">REGEX</regex>
    <comment>COMMENT HERE</comment>
</hint>

To require a form:

<hint>
    <regex present="required">REGEX</regex>
    <comment>COMMENT HERE</comment>
</hint>

General hint structure:

<hint>
    <regex present="ATTRIBUTE">REGEX</regex>
    <comment>COMMENT</comment>
</hint>

ATTRIBUTE is one of: required, forbidden, necessary, allowed, encouraged, discouraged.

For multiple variables, create one <question> per variable, each with a unique key.
Each question must have its own <expression>.

The <expression> tag contains only the target expression and no equal sign.

Enclose the entire XML in:

<pre><code>
...
</code></pre>