Literals & Adjacency

Text you meant as literal stays literal, and two adjacent tokens never silently merge into a different token when the output is read back. rosetta-date calls this guarantee round-trip safety at the token boundary.

Literals

Literal (verbatim) text is preserved across dialects, even though each dialect escapes it differently:

• moment brackets [...] ↔ ldml quotes '...'.
• A literal apostrophe is '' in ldml (e.g. 'o''clock' → o'clock).
• Only the letter-bearing span is escaped, so separators stay clean: DD/MM ↔ dd/MM, not dd'/'MM.
• A literal ] has no in-band escape inside a moment [...] run, so it is emitted between bracketed spans (e.g. a]b → [a]][b]); the text still round-trips intact.

Adjacent tokens

When a conversion would place two tokens that collide — i.e. reading the output back would lex them as one different token — rosetta-date separates them with the target dialect’s empty literal.

For example, date-fns PPPp (a long date next to a short time) becomes moment LL + LT. But gluing them as LLLT would re-read as LLL (the long localized date preset) + T, a different parse. So the converter inserts []:

import { convert } from 'rosetta-date'
import { dateFns, momentjs } from 'rosetta-date/libraries'
 
convert('PPPp', { from: dateFns, to: momentjs }) // 'LL[]LT' — '[]' keeps LL and LT apart

When a dialect has no empty literal

A quote-style dialect like ldml has no empty literal — '' is a literal apostrophe, not nothing — so it cannot express such an adjacency. There the second token is routed through onUnsupportedToken with reason unrepresentable-adjacency:

• the default emits it anyway (matching the merged output), while
• 'throw' lets a mass migration catch it.