Add documentation on how to access math functions in code (#458)

docs/src/reference/details.yml

@@ -85,6 +85,16 @@ math: |
   Functions calls preceded by a hashtag are normal code function calls and not
   affected by these rules.
 
+  All math functions are part of the `math` [module]($scripting/#modules), which
+  is available by default in equations. Outside of equations, they can be
+  accessed with the `math.` prefix. For example, to set the font used for
+  equations, write:
+
+  ```example
+  #show math.equation: set text(font: "Fira Math")
+  $ sum_(i in NN) 1 + i $
+  ```
+
 layout: |
   Arranging elements on the page in different ways.
 
@@ -124,6 +134,7 @@ sym: |
   prefix.
 
   The `d` in an integral's `dx` can be written as `[$dif x$]`.
+  Outside math formulas, `dif` can be accessed as `math.dif`.
 
 emoji: |
   Named emoji.