What HTML is
An HTML table is a table element containing thead and tbody, with th cells for headers and td cells for data.
Web pages, email templates and anything pasted into a CMS.
What Textile is
Textile marks header cells with |_. and data cells with plain pipes.
Redmine, and older Rails applications.
What changes when you convert HTML to Textile
The first table in the markup is used. Cell contents are stripped of inline tags and entities are decoded, so <td><b>Total</b> </td> arrives as Total. Nested tables inside a cell are not descended into.
The header row is written with the |_. marker so it renders as a header.
What carries over from HTML to Textile
HTML records 3 things about a table that Textile has no way to hold.
HTML can hold a value that is itself a list or an object. Textile has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
A line break inside a cell ends the row in Textile, so line breaks are replaced rather than carried through.
Anything visual in the HTML - weight, alignment, colour, column widths - has no counterpart in Textile and is dropped. The values are what survives.
The identifier 007 comes out of the Textile as 007. Reading it as a number would have made it 7, and an id that changes value is worse than one that stays text.
The role "Analyst, data" survives with its comma, in one cell rather than split across two. That is the first thing to check in any converted table, and the usual place a Textile file goes wrong.
The quotes around Jonah "Jo" Pryce are left as a plain quote character in the Textile.