* [`==` and `!=`](/documentation/operators/equality) are used to check if two
  values are the same.
* [`+`, `-`, `*`, `/`, and `%`](/documentation/operators/numeric) have their
  usual mathematical meaning for numbers, with special behaviors for units that
  matches the use of units in scientific math.
* [`<`, `<=`, `>`, and `>=`](/documentation/operators/relational) check whether
  two numbers are greater or less than one another.
* [`and`, `or`, and `not`](/documentation/operators/boolean) have the usual
  boolean behavior. Sass considers every value "true" except for `false` and
  `null`.
* [`+`, `-`, and `/`](/documentation/operators/string) can be used to
  concatenate strings.
<% if parens %>
* [`(` and `)`](/documentation/operators#parentheses) can be used to explicitly
  control the precedence order of operations.
<% end %>