The SDLXLIFF files which Passolo are just exporting, do not contain any placeholders/variable tags like ‘{1}’ or '%d' or embedded HTML/XML markup, all show as ‘Plain Text’ rather than placeholders where direct impact word counts and open as editable strings.
It would be perfectly good as workaround solution in Studio setting for ‘SDL XLIFF’ (supporting for .sdlxliff) to be able to add tag rule for regular expression upfront and store them into a Studio project. Similar idea with current Studio setting as normal ‘XLIFF’ setting where has the Embedded content feature.