diff --git a/libsolidity/AST.h b/libsolidity/AST.h
index d2fb15a45..10616022b 100644
--- a/libsolidity/AST.h
+++ b/libsolidity/AST.h
@@ -98,19 +98,21 @@ private:
 
 /**
  * Import directive for referencing other files / source objects.
+ * Example: import "abc.sol"
+ * Source objects are identified by a string which can be a file name but does not have to be.
  */
 class ImportDirective: public ASTNode
 {
 public:
-	ImportDirective(Location const& _location, ASTPointer<ASTString> const& _url):
-		ASTNode(_location), m_url(_url) {}
+	ImportDirective(Location const& _location, ASTPointer<ASTString> const& _identifier):
+		ASTNode(_location), m_identifier(_identifier) {}
 
 	virtual void accept(ASTVisitor& _visitor) override;
 
-	ASTString const& getURL() const { return *m_url; }
+	ASTString const& getIdentifier() const { return *m_identifier; }
 
 private:
-	ASTPointer<ASTString> m_url;
+	ASTPointer<ASTString> m_identifier;
 };
 
 /**
diff --git a/libsolidity/ASTPrinter.cpp b/libsolidity/ASTPrinter.cpp
index c62378fd3..3d09fd9af 100644
--- a/libsolidity/ASTPrinter.cpp
+++ b/libsolidity/ASTPrinter.cpp
@@ -45,7 +45,7 @@ void ASTPrinter::print(ostream& _stream)
 
 bool ASTPrinter::visit(ImportDirective& _node)
 {
-	writeLine("ImportDirective \"" + _node.getURL() + "\"");
+	writeLine("ImportDirective \"" + _node.getIdentifier() + "\"");
 	printSourcePart(_node);
 	return goDeeper();
 }
diff --git a/libsolidity/CompilerStack.cpp b/libsolidity/CompilerStack.cpp
index 621723848..20b0b3e57 100644
--- a/libsolidity/CompilerStack.cpp
+++ b/libsolidity/CompilerStack.cpp
@@ -201,12 +201,12 @@ void CompilerStack::resolveImports()
 		for (ASTPointer<ASTNode> const& node: _source->ast->getNodes())
 			if (ImportDirective const* import = dynamic_cast<ImportDirective*>(node.get()))
 			{
-				string const& url = import->getURL();
-				if (!m_sources.count(url))
+				string const& id = import->getIdentifier();
+				if (!m_sources.count(id))
 					BOOST_THROW_EXCEPTION(ParserError()
 										  << errinfo_sourceLocation(import->getLocation())
 										  << errinfo_comment("Source not found."));
-				toposort(&m_sources[url]);
+				toposort(&m_sources[id]);
 			}
 		sourceOrder.push_back(_source);
 	};
diff --git a/libsolidity/CompilerStack.h b/libsolidity/CompilerStack.h
index 34178841a..bedb4cc38 100644
--- a/libsolidity/CompilerStack.h
+++ b/libsolidity/CompilerStack.h
@@ -66,7 +66,7 @@ public:
 	/// Returns a list of the contract names in the sources.
 	std::vector<std::string> getContractNames();
 
-	/// Compiles the source units that were prevously added and parsed.
+	/// Compiles the source units that were previously added and parsed.
 	void compile(bool _optimize = false);
 	/// Parses and compiles the given source code.
 	/// @returns the compiled bytecode
diff --git a/libsolidity/NameAndTypeResolver.cpp b/libsolidity/NameAndTypeResolver.cpp
index 08deb66a0..3715df6ad 100644
--- a/libsolidity/NameAndTypeResolver.cpp
+++ b/libsolidity/NameAndTypeResolver.cpp
@@ -40,6 +40,7 @@ NameAndTypeResolver::NameAndTypeResolver(std::vector<Declaration*> const& _globa
 
 void NameAndTypeResolver::registerDeclarations(SourceUnit& _sourceUnit)
 {
+	// The helper registers all declarations in m_scopes as a side-effect of its construction.
 	DeclarationRegistrationHelper registrar(m_scopes, _sourceUnit);
 }