Comment 142 for bug 10883

Then, the template for localized UI strings lives in dtd files (for dynamic strings, in properties files), so whereever you have visible strings in your UI, you outsource those to here, e.g. label="&stringEntityID;"

https://dxr.mozilla.org/comm-central/source/mail/locales/en-US/chrome/messenger/messengercompose/messengercompose.dtd