Add docs

boa_engine/src/bytecompiler.rs

@@ -2377,6 +2377,11 @@ impl<'b> ByteCompiler<'b> {
         Ok(has_identifier_argument)
     }
 
+    /// This function compiles a class declaration or expression.
+    ///
+    /// The compilation of a class declaration and expression is mostly equal.
+    /// A class declaration binds the resulting class object to it's identifier.
+    /// A class expression leaves the resulting class object on the stack for following operations.
     fn class(&mut self, class: &Class, expression: bool) -> JsResult<()> {
         let mut code = CodeBlock::new(class.name(), 0, true, true);
         code.computed_field_names = Some(gc::GcCell::new(vec![]));

boa_engine/src/vm/opcode.rs

@@ -531,14 +531,14 @@ pub enum Opcode {
     /// Stack: value, key, object **=>**
     SetPropertyByValue,
 
-    /// Defines a class method by value.
+    /// Defines a own property of an object by value.
     ///
     /// Operands:
     ///
     /// Stack: object, key, value **=>**
     DefineOwnPropertyByValue,
 
-    /// Defines a own property of an object by value.
+    /// Defines a class method by value.
     ///
     /// Operands:
     ///