diff --git a/assembler/assembler/assembler.py b/assembler/assembler/assembler.py
index 53f556c..f4dbbe6 100644
--- a/assembler/assembler/assembler.py
+++ b/assembler/assembler/assembler.py
@@ -108,24 +108,20 @@ class Assembler(object):
 		if(token in self._marks):
 			if(self._marks[token]["target"] != -1):
 				raise ParsingError("Error in line {} column {} mark already defined: '{}'. Previous was in line {}.".format(
-						self._line
+						self._file_context._line
 						, self._column
 						, token
 						, self._marks[token]["target_line"]))
 			self._marks[token]["target"] = self._word_count
-			self._marks[token]["target_line"] = self._line
+			self._marks[token]["target_line"] = self._file_context._line
 
 		else:
 			self._marks[token] = {
 				"target": self._word_count
-				, "target_line": self._line
+				, "target_line": self._file_context._line
 				, "references": []
 			}
 
-		should_be_newline = next(self._tokenizer)
-		if(should_be_newline != "\n"):
-			self.raise_unexpected_token(token, "newline", should_be_newline)
-
 
 	def parse_directive(self):
 		should_be_name = next(self._tokenizer)
@@ -133,6 +129,10 @@ class Assembler(object):
 		if(not should_be_name in self._directives):
 			self.raise_unexpected_token(".", "directive name", should_be_name)
 
+		should_be_whitespace = next(self._tokenizer)
+		if(not should_be_whitespace in WHITESPACE):
+			self.raise_unexpected_token(should_be_name, "' '", should_be_whitespace)
+
 		words = self._directives[should_be_name].parse(self, self._tokenizer)
 		
 		self._word_count += len(words)
@@ -146,16 +146,16 @@ class Assembler(object):
 
 
 	def parse_command(self, cmd):
-
-		self._code_objects.append(self._opcodes[cmd])
-		self._word_count += 1
-
+		# We have no arguments
 		if(not self._commands_by_mnemonic[cmd]["args"]):
+			self._code_objects.append(self._opcodes[cmd])
+			self._word_count += 1
 			token = next(self._tokenizer)
 			if(token != "\n"):
 				self.raise_unexpected_token(cmd, "newline", token)
 			return 
 
+		# Small argument must be treated separately
 		should_be_whitespace = next(self._tokenizer)
 		if(should_be_whitespace not in WHITESPACE 
 				or should_be_whitespace == "\n"):
@@ -166,9 +166,12 @@ class Assembler(object):
 				, should_be_an_argument
 				, self._commands_by_mnemonic[cmd]["args"][0])
 		self._word_count += 1
-		self._code_objects.append(argument)
+		# NOTE:
+		# The Small Argument is stored within the first word (!)
+		self._code_objects.append(self._opcodes[cmd] | (argument & 0xffff))
 		
 
+		# All the 16bit arguments
 		for argument in self._commands_by_mnemonic[cmd]["args"][1:]:
 			should_be_comma = next(self._tokenizer)
 			if(should_be_comma != ","):
@@ -239,22 +242,31 @@ class Assembler(object):
 			return argument
 
 		if(argument_definition == "program_memory"):
+			# Non-integer Argument.
 			if(not can_convert_to_int(argument)):
+				# Just nonsense.
 				if(not can_be_mark(argument)):
 					self.raise_unexpected_token(cmd, "integer address or mark", argument)
+				# The Mark has appeared before.
 				if(argument in self._marks):
-					self._marks[argument]["references"].append(self._line)
+					# Add this line to the references.
+					self._marks[argument]["references"].append(self._file_context._line)
+					# The target is already known. Insert it now.
 					if(self._marks[argument]["target"] != -1):
 						return self._marks[argument]["target"]
+					# The target is unknown.
 					return argument
+				# The Mark has not appeared before.
 				self._marks[argument] = {
 					"target": -1
 					, "target_line": 0
-					, "references": [self._line]
+					, "references": [self._file_context._line]
 				}
+				# Target is obviously unknown.
 				return argument
 
 
+			# Integer argument.
 			argument = autoint(argument)
 
 			if(argument < 0 or argument > self._memory_definition["program_memory"]):
@@ -264,17 +276,29 @@ class Assembler(object):
 						, argument)
 			return argument
 
+		# This is direct input (default).
 
+		# Integer
 		if(can_convert_to_int(argument)):
 			return autoint(argument)
 
+		# This is nonsense.
 		if(not can_be_mark(argument)):
 			self.raise_unexpected_token(cmd, "integer, char or mark", argument)
-		if(argument in self._marks and self._marks[argument] >= 0):
-			return self._marks[argument]
-		self._marks[argument] = -1
+
+		# It is a Mark.
+		if(argument in self._marks):
+			if(self._marks[argument]["target"] >= 0):
+				self._marks[argument]["references"].append(self._file_context._line)
+				return self._marks[argument]["target"]
+			self._marks[argument]["references"].append(self._file_context._line)
+			return argument
+			
+		self._marks[argument] = {
+			"target": -1
+			, "target_line": 0
+			, "references": [self._file_context._line]
+		}
+
 		return argument
 
-
-			
-
diff --git a/assembler/assembler/directives.py b/assembler/assembler/directives.py
index 24b6c99..a03383d 100644
--- a/assembler/assembler/directives.py
+++ b/assembler/assembler/directives.py
@@ -5,6 +5,8 @@ Directives for explicitly modifying the program memory.
 from abc import ABC, abstractmethod
 from collections import deque
 
+from .util import can_convert_to_int, autoint
+
 class AbstractDirective(ABC):
 	@abstractmethod
 	def parse(self, assembler, tokenizer):
diff --git a/assembler/test/test_011_tokenize.py b/assembler/test/test_011_tokenize.py
index 2a2955c..590d13f 100644
--- a/assembler/test/test_011_tokenize.py
+++ b/assembler/test/test_011_tokenize.py
@@ -52,3 +52,20 @@ def test_tokenize_3():
 		, "string", ":", "\n"
 		, ".", "set", " ", "[", "'h'", ",", "'e'", ",", "'l'", ",", "'l'", ",", "'o'", "]", "\n"
 		]
+
+def test_tokenize_4():
+	data = '''
+	ldi r0, 0xfefe
+	test_mark:
+	ldi r1, 0xefef
+	'''
+	data = StringIO(data)
+	tokenizer = Tokenizer(FileContext(data))
+
+	result = list(tokenizer)
+
+	assert result == [
+		"ldi", " ", "r0", ",", "0xfefe", "\n"
+		, "test_mark", ":", "\n"
+		, "ldi", " ", "r1", ",", "0xefef", "\n"
+		]
diff --git a/assembler/test/test_020_basic_parsing.py b/assembler/test/test_020_basic_parsing.py
index 9e89eb9..0b1a569 100644
--- a/assembler/test/test_020_basic_parsing.py
+++ b/assembler/test/test_020_basic_parsing.py
@@ -17,6 +17,52 @@ def test_commands(basic_machine_definition):
 	assembler = Assembler(data, memory_definition, command_defintion, {})
 	assembler.parse()
 
-	assert assembler._code_objects == [32704, 0, 0xfe
-					, 32704, 1, 0xfe
-					, 40896, 0, 1]
+	assert assembler._code_objects == [32704 | 0, 0xfe
+					, 32704 | 1, 0xfe
+					, 40896 | 0, 1]
+
+def test_mark(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, test_mark
+		ldi r1, 0xfe
+		test_mark:
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+	assembler.parse()
+
+
+	assert assembler._code_objects == [32704 | 0, 4
+					, 32704 | 1, 0xfe
+					, 40896 | 0, 1]
+
+
+def test_set_directive(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, test_mark
+		ldi r1, 0xfe
+		test_mark:
+		.set [0xfe, 0xef,
+			10, 20,
+			'a', 'b',
+			'\\n', 0b10]
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+	assembler.parse()
+
+
+	assert assembler._code_objects == [32704 | 0, 4
+					, 32704 | 1, 0xfe
+					, 0xfe, 0xef
+					, 10, 20
+					, ord("a"), ord("b")
+					, ord("\n"), 0b10]
+