What to paste

PECTAB required: The format table itself. It begins PT for a boarding pass or BTT for a bag tag, and the device is recognised from that — there is nothing to choose.
Template optional, boarding pass only: The TT table holding the static artwork: lines, boxes, logos and fixed text. Supplying it draws that artwork in alongside the variable data.
Data optional: A live boarding pass or bag tag message. It replaces generic element names with the real values, so you see what the passenger would be handed, and it points out any element the message carries that the PECTAB does not define.

The Load example buttons fill all three with a known-good set.

The mock-up

Black is printed content; red is the template overlay.
The grid is a ruler, not part of the stock. The solid blue lines carry the row letters and column numbers; the dotted green ones fill in between.
Barcodes are encoded for real, not drawn from pictures. One that cannot be encoded — letters in a numbers-only symbology, say — is outlined with a dashed box and the reason appears in its explanation and on hover.
A logo is drawn as a frame at a nominal size. The PECTAB carries only the logo's number, so its printed extent cannot be known here; the bottom-left corner it is labelled in is the print anchor, and that is exact.

Every element is listed with an explanation of what it prints and where, beside a to-scale mock-up of the stock.

Click an element — its explanation or its text — and the mock-up marks exactly where it prints. Click it on the mock-up and the list scrolls to it.
Edit an element's text and the mock-up redraws as you type.
Drag an element on the mock-up and its coordinates are rewritten for you. Boarding pass elements snap back inside the stock; bag tag elements may sit outside the printable area, because real ones do.

Duplicate element: Copies the element you have selected. On a bag tag or a template that is a new element sharing the original's content; on a boarding pass it is a second place the same element prints, because one ATB element can print at as many positions as it likes. Remove an element with the × beside its text.
Sort: Puts elements in the order they print, top to bottom then left to right. On a bag tag it renumbers the PECTAB's elements; only those whose number does not decide their content are moved, and if one that must keep its number sits where the others would be renumbered to, it says so and changes nothing. On a boarding pass the PECTAB's order is fixed by the specification, so Sort orders the template instead and renumbers it from 01. It is held while an edit is outstanding and released once the mock-up has caught up.
Revert changes: Back to the PECTAB you arrived with.
Print: The mock-up first, then every element with its explanation.
Pack up: Returns to Home with your edits recombined into a single PECTAB string, ready to load into printers.