Static start of a translation key built at runtime ('A.' + x, `A.${x}`).
'A.' + x
`A.${x}`
0-based offset of the key expression in the template text.
Static start of the key, e.g. A. for 'A.' + x.
A.
Translation pipe or translation directive.
Static start of a translation key built at runtime (
'A.' + x,`A.${x}`).