Improves inline documentation

apollo-ios-codegen/Sources/IR/GraphQLCompositeType+Identifiable.swift

@@ -1,6 +1,7 @@
 import GraphQLCompiler
 
 extension GraphQLCompositeType {
+  /// Indicates if the type has a single keyField named `id`.
   var isIdentifiable: Bool {
     switch(self) {
     case let interface as GraphQLInterfaceType:

apollo-ios-codegen/Sources/IR/IR+ComputedSelectionSet.swift

@@ -20,7 +20,8 @@ public struct ComputedSelectionSet {
   /// The `TypeInfo` for the selection set of the computed selections
   public let typeInfo: IR.SelectionSet.TypeInfo
 
-  /// Indicates if the parent type has a single keyField named `id`.
+  /// Indicates if a field named `id` is selected as well as requiring that the parent type
+  /// be identifiable.
   public var isIdentifiable: Bool {
     guard direct?.fields["id"] != nil || merged.fields["id"] != nil else {
       return false

apollo-ios-codegen/Sources/IR/IR+NamedFragment.swift

@@ -23,7 +23,8 @@ public class NamedFragment: Definition, Hashable, CustomDebugStringConvertible {
   public var type: GraphQLCompositeType { definition.type }
   public var isLocalCacheMutation: Bool { definition.isLocalCacheMutation }
 
-  /// Indicates if the parent type has a single keyField named `id`.
+  /// Indicates if a field named `id` is selected as well as requiring that the parent type
+  /// be identifiable.
   public var isIdentifiable: Bool {
     guard definition.selectionSet.selections.contains(where: {
       guard case .field(let field) = $0 else { return false }