Expand @static docstring

Author: Sbozzolo

base/osutils.jl

@@ -5,11 +5,18 @@
 
 Partially evaluate an expression at parse time.
 
-For example, `@static Sys.iswindows() ? foo : bar` will evaluate `Sys.iswindows()` and insert
-either `foo` or `bar` into the expression.
-This is useful in cases where a construct would be invalid on other platforms,
-such as a `ccall` to a non-existent function.
-`@static if Sys.isapple() foo end` and `@static foo <&&,||> bar` are also valid syntax.
+This is useful in cases where a construct would be invalid in some cases, such as a `ccall`
+to a os-dependent function, or macros defined in packages that are not imported.
+
+`@static` requires a conditional. The conditional can be in an `if` statement, a ternary
+operator, or `&&`\`||`.
+
+# Example
+
+Suppose we want to parse an expression `expr` that is valid only on MacOS. We could solve
+this problem using `@static` with `@static if Sys.isapple() expr end`. In case we had
+`expr_apple` for MacOS and `expr_others` for the other operating systems, the solution with
+`@static` would be `@static Sys.isapple() ? expr_apple : expr_others`.
 """
 macro static(ex)
     if isa(ex, Expr)