In XLIFF, we generate an ID for each placeholder from its position in the source template. This lets us reliably track placeholders if they change position in a translated template.

For XLB, we don't currently generate an ID at all, so we use the placeholder text itself as the ID. This is fine most of the time, but could fail in some weird edge cases where two identical placeholders appear, but their order actually matters (e.g. a template with an expression ${i++}).

Maybe we can use the XLB name attribute for this, but we need to think about what this would mean for translators, because this might cause them to see a numeric ID instead of the placeholder contents.