Concatenate any mix of plain strings and Instructions, propagating
both audio/text variants. If no argument is an Instructions the
result is a plain string; otherwise the result is an Instructions
preserving both variants from every contributing operand.
Concatenate any mix of plain strings and Instructions, propagating both audio/text variants. If no argument is an Instructions the result is a plain string; otherwise the result is an Instructions preserving both variants from every contributing operand.