Treat empty lines as structure
A caption may contain multiple text lines, but a blank separator line has a structural role in WebVTT. Adding an empty paragraph for visual breathing room can end the cue block instead of adding spacing inside it.
The W3C WebVTT Candidate Recommendation Draft of 20 May 2026 defines file structure and parsing separately. A tolerant parser recovering some text does not establish that the exported file is correctly authored.
Keep an export that reveals whitespace
For an invented two-line cue, preserve the single line break between the phrases. If a formatter inserts an additional empty line, inspect the parsed cues and remaining text. Do not rely on the source document looking tidier in a general-purpose editor.
The same boundary matters when WebVTT carries metadata. Pretty-printing a payload with blank lines can change its block structure. Use a serialisation rule that respects the containing format, not merely the conventions of the embedded data.
Verify after automatic processing
Include caption files in checks after templating, line-ending conversion or content-management export. A process intended for ordinary prose may trim, wrap or expand whitespace. Save the exported file and a small parsed cue inventory so the effect can be reviewed.
If the intended visual layout needs more space, use supported presentation mechanisms and check the final result. Do not use empty source paragraphs as an undocumented substitute. No file in this example was passed through a real player; it is an authored export review.
Questions answered
Is one line break inside cue text the same as a blank line?
No. A blank separator line has a block-boundary role.
Does partial rendering prove the file was valid?
No. Parser recovery and authoring conformance are different checks.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.