What the Reader shows

One layout per record shape

Email

headersFrom, To, Cc, Date, Message-IDShown as text nodes, never as markup.
below the headersBody text and the attachment listAn HTML body is displayed as its source.

Attachment

headerName, type and sizePlus a link back to the email it came from.
bodyExtracted text of that pageax_locator att0-p3-s0 is page 3 of the first attachment.

PDF page

headerTitle and page numberA long PDF becomes many records, one per page section.
bodyThat page's textThe Reader renders no PDF page, only its text.

File

headerPath and formatThe same-folder and link detectors connect file records.
bodyEvery record from that fileThey share one ax_file value.
The four record shapes the Reader renders, from the console reader use case in the repository. Every record that came out of one .eml file carries the same ax_file, and the Reader joins on it.