Add comments to an expression

If you write a complex expression and intend for you or someone else to use it later, you should add comments that explain what the expression does and how its pieces work.

Type // at the beginning of the comment. Any text between // and the end of the line is ignored. For example:
```
  // This is a comment.
```
For examples of this type of comment, see Example: Fade opacity of a 3D layer based on distance from camera.
Type /* at the beginning of the comment and */ at the end of the comment. Any text between /* and */ is ignored. For example:
```
  /*  This is a   
      multiline comment. */
```
For examples of this type of comment, see Save and reuse expressions.