Allow manipulation of comments in the Script Info section

src/ass/document.py

@@ -90,7 +90,13 @@ def parse_file(cls, f):
                                      " usually '%s'" % cls.PREFERRED_ENCODING.name)
 
             line = line.strip()
-            if not line or line.startswith(';'):
+            if not line:
+                continue
+
+            if line.startswith(';'):
+                # ";" comments only permitted in Script Info section, ignore otherwise
+                if section == doc.sections.get("Script Info"):
+                    section.add_comment(line[1:])
                 continue
 
             if line.startswith('[') and line.endswith(']'):

src/ass/section.py

@@ -84,6 +84,11 @@ def add_line(self, field_name, field):
     def dump(self):
         yield "[{}]".format(self.name)
 
+        # Comments are customarily at the beginning
+        if hasattr(self, "comments"):
+            for c in self.comments:
+                yield ";{}".format(c)
+
         for k, v in self._fields.items():
             yield "{}: {}".format(k, _Field.dump(v))
 
@@ -149,3 +154,10 @@ class ScriptInfoSection(FieldSection):
         "WrapStyle": _Field("WrapStyle", int, default=0),
         "ScaledBorderAndShadow": _Field("ScaledBorderAndShadow", str, default="yes")
     }
+
+    def add_comment(self, comment):
+        self.comments.append(comment)
+
+    def __init__(self, name, fields=None):
+        super().__init__(name, fields=fields)
+        self.comments = []