To get a side-by-side preview of a term-translation pair containing HTML or Markdown syntax, go to the desired language page and hover your mouse over a translation with such elements. If we detect HTML or Markdown syntax in said translation, an eye icon will appear at the end of the string. Click on it to see the preview.
Any member of a localization project can preview the strings containing HTML or Markdown, to make sure that no syntax errors slipped in the translated string.