diff --git a/PyTeX/format/generic_text.py b/PyTeX/format/generic_text.py
index 27a9d72..89bf78a 100644
--- a/PyTeX/format/generic_text.py
+++ b/PyTeX/format/generic_text.py
@@ -65,7 +65,7 @@ class GenericText:
         lines = []
         for line in self.text:
             try:
-                line = '% ' + line.format(**kwargs).rjust(77) + '%'
+                line = '% ' + line.rstrip().format(**kwargs).ljust(77) + '%'
                 if len(line) > 80:
                     logger.warning(
                         'Line too long')  # TODO
@@ -96,7 +96,10 @@ class GenericText:
 
     def __iadd__(self, other: Union[None, GenericText, List[str]]) -> GenericText:
         if not self.has_value():
-            self.text = other
+            if isinstance(other, GenericText):
+                self.text = other.text
+            else:
+                self.text = other
         elif isinstance(other, GenericText):
             if other.has_value():
                 self.text += other.text
diff --git a/PyTeX/format/pytex_formatter.py b/PyTeX/format/pytex_formatter.py
index 48cdba9..fa1bcfd 100644
--- a/PyTeX/format/pytex_formatter.py
+++ b/PyTeX/format/pytex_formatter.py
@@ -149,9 +149,9 @@ class PyTeXFormatter(FormatterIF, ABC):
             FormatterProperty.pytex_branch.value: self.git_version_info.pytex_version.branch,
             FormatterProperty.pytex_commit.value: self.git_version_info.pytex_version.commit_hash,
             FormatterProperty.pytex_dirty.value: self.git_version_info.pytex_version.dirty,
-            FormatterProperty.tex_type.value: str(self.config.tex_type),
-            FormatterProperty.tex_flavour.value: str(self.config.tex_flavour),
-            FormatterProperty.file_prefix.value: str(self.file_prefix)
+            FormatterProperty.tex_type.value: self.config.tex_type.value,
+            FormatterProperty.tex_flavour.value: self.config.tex_flavour.value,
+            FormatterProperty.file_prefix.value: self.file_prefix
         }
 
     @property
@@ -199,11 +199,14 @@ class PyTeXFormatter(FormatterIF, ABC):
         return self._output_file.name
 
     def make_header(self, **kwargs) -> str:
-        return '\n'.join(
-            [
-                '%' * 80,
-                self.header.format(**kwargs),  # TODO: add standard keywords here
-                '%' * 80,
-                ''
-            ]
-        )
+        try:
+            return '\n'.join(
+                [
+                    '%' * 80,
+                    self.header.format(**self.attribute_dict),
+                    '%' * 80,
+                    ''
+                ]
+            )
+        except KeyError:
+            raise NotImplementedError