Documentation: add class comments

src/UnifiedFFI/FFIClassVariableArgument.class.st

@@ -1,3 +1,6 @@
+"
+I am a loader for class variables, pushing to the stack the class variable literal
+"
 Class {
 	#name : #FFIClassVariableArgument,
 	#superclass : #FFIFunctionArgumentLoader,

src/UnifiedFFI/FFIConstantArgument.class.st

@@ -1,3 +1,10 @@
+"
+I am a function argument representing a literal value (in contrast to a variable).
+The parser creates me when it finds other than symbols as arguments.
+
+I am resolved by resolving my type.
+The type knows how to resolve itself in a context.
+"
 Class {
 	#name : #FFIConstantArgument,
 	#superclass : #FFIFunctionArgument,

src/UnifiedFFI/FFITypeDeclaration.class.st

@@ -1,3 +1,7 @@
+"
+I represent a type declaration in a FFI function signature. I have a type name and an arity (the number of indirections indicated by pointer marker stars *).
+I am resolved as an external FFI type with my arity.
+"
 Class {
 	#name : #FFITypeDeclaration,
 	#superclass : #Object,

src/UnifiedFFI/FFIUndefinedTypeDeclaration.class.st

@@ -1,3 +1,10 @@
+"
+I represent the absense of a type declaration.
+I delegate my resolution to the resolver with a double dispatch so it can choose how to resolve non-declared types.
+A resolver (FFICallout) has two main resolution strategies: 
+- strict does not accept resolving undefined types
+- non strict is a backwards compatibility mode that tries to infer the type if possible (but can go wrong and should be used with care)
+"
 Class {
 	#name : #FFIUndefinedTypeDeclaration,
 	#superclass : #Object,

src/UnifiedFFI/FFIVariableArgument.class.st

@@ -1,3 +1,11 @@
+"
+I am a function argument representing a variable (in contrast to a literal value).
+The parser creates me when it finds symbols as arguments.
+
+I am resolved by resolving my type and my name.
+The type knows how to resolve itself in a context.
+To resolve my name, the resolver performs a semantic analysis in the calling context to define if the variable is an instance variable, a method argument or a class variable. The name resolution is represented by my loader.
+"
 Class {
 	#name : #FFIVariableArgument,
 	#superclass : #FFIFunctionArgument,