Document using the element editor -- drawing tools, not just the resulting XML sources/editor/ is ~22,900 lines and the only wiki coverage was a stub telling readers to see the elements_XML reference for 'designing element graphics' and 'defining connection terminals' -- which documents the file format an element becomes, not how to use the editor that draws it. element_linking already covers the master/slave/terminal semantics; this covers the tool itself. The finding worth having written down: width, height and hotspot have no input dialog at all. ElementScene::toXml() derives them from the drawn geometry on every save -- bounding rect rounded up to the next multiple of 10 (with a quirk: a remainder over 6 rounds up an extra ten, which is exactly the 42-to-50 example elements_definition_attribute.md already used without explaining where the number came from), hotspot centered in that box. And if the drawing doesn't straddle the scene origin, centerElementToOrigin() actually moves every primitive on save, not just the saved coordinates -- draw far from the crosshair and a save visibly shifts everything. Also: the checkElement() validation that runs before every save (0 terminals warns but doesn't block, except folio-report and conductor-definition elements, which must have exactly one or the save is refused); the Save vs Save As vs Save As File distinction (opened-from location vs a collection picker vs a raw file picker); and the terminal placement shortcuts (Space rotates through the four orientations while placing, the tool re-arms at the same orientation for a row of pins). Replaces the empty 'Creating Custom Elements' stub in user_manual (all three languages) with links to this page, element_linking and elements_XML instead of a four-bullet list pointing at one reference page. EN/FR/DE.