Transforms needed by most or all documents:
- `Decorations`: Generate a document's header & footer.
- `ExposeInternals`: Expose internal attributes.
- `Messages`: Placement of system messages generated after parsing.
- `FilterMessages`: Remove system messages below verbosity threshold.
- `TestMessages`: Like `Messages`, used on test runs.
- `StripComments`: Remove comment elements from the document tree.
- `StripClassesAndElements`: Remove elements with classes
in `self.document.settings.strip_elements_with_classes`
and class values in `self.document.settings.strip_classes`.
- `SmartQuotes`: Replace ASCII quotation marks with typographic form.