Where can I find good documentation about the Text Ruler?

If you select text in a field and apply any kind of styling the information is stored as a Character style and/or Paragraph style for the text. That is metadata, and because it is associated with the data you will not find that information in the DDR or XML copy. You will find it on the clipboard when you cut or copy the data.

You can apply character styles and paragraph styles to the field in layout mode. These are stored in Local Styles or in the selected theme. You will find these in the DDR or XML copy.