swc-project/swc · warning · Error

Non-space character after "frameset"

Error message

Non-space character after "frameset"

What it means

A non-whitespace character token was dispatched in the 'after frameset' insertion mode. The spec says: parse error, ignore the token — text after the frameset is closed is dropped from the tree entirely. NonSpaceCharacterAfterFrameset records the discarded text with its span.

Source

Thrown at crates/swc_html_parser/src/parser/mod.rs:6521

                    // Process the token using the rules for the "in head" insertion mode.
                    Token::StartTag { tag_name, .. } if tag_name == "noframes" => {
                        self.process_token_using_rules(token_and_info, InsertionMode::InHead)?;
                    }
                    // An end-of-file token
                    //
                    // Stop parsing.
                    Token::Eof => {
                        self.stopped = true;
                    }
                    // Anything else
                    //
                    // Parse error. Ignore the token.
                    _ => match token {
                        // Doctype handled above
                        // Comment handled above
                        // EOF handled above
                        Token::Character { .. } => {
                            self.errors.push(Error::new(
                                token_and_info.span,
                                ErrorKind::NonSpaceCharacterAfterFrameset,
                            ));
                        }
                        Token::StartTag { tag_name, .. } => {
                            self.errors.push(Error::new(
                                token_and_info.span,
                                ErrorKind::StrayStartTag(tag_name.clone()),
                            ));
                        }
                        Token::EndTag { tag_name, .. } => {
                            self.errors.push(Error::new(
                                token_and_info.span,
                                ErrorKind::StrayEndTag(tag_name.clone()),
                            ));
                        }
                        _ => {
                            unreachable!()

View on GitHub (pinned to 5176682b65)

Solutions

  1. Remove the trailing text, or relocate it into a <noframes> block or the frame's own document.
  2. Fix include order so appended content lands inside a frame target, not after </frameset>.
  3. If third-party, filter ErrorKind::NonSpaceCharacterAfterFrameset; note the text is dropped, not relocated.

Example fix

<!-- before -->
<frameset cols="*"><frame src="a.html"></frameset>
Copyright 2026 Acme
</html>

<!-- after -->
<frameset cols="*">
  <frame src="a.html">
  <noframes>Copyright 2026 Acme</noframes>
</frameset>
</html>
Defensive patterns

Strategy: validation

Validate before calling

// Non-whitespace text between </frameset> and </html> (or EOF).
fn has_text_between(src: &str, start_close: &str, end_close: &str) -> bool {
    let lower = src.to_ascii_lowercase();
    if let Some(s) = lower.find(start_close) {
        let rest = &lower[s + start_close.len()..];
        let end = rest.find(end_close).unwrap_or(rest.len());
        return rest[..end].chars().any(|c| !c.is_ascii_whitespace() && c != '<');
    }
    false
}
// has_text_between(&html, "</frameset>", "</html>")

Type guard

use swc_html_parser::error::{Error, ErrorKind};

fn is_non_space_after_frameset(err: &Error) -> bool {
    matches!(err.kind(), ErrorKind::NonSpaceCharacterAfterFrameset)
}

Try / catch

let mut errors = Vec::new();
let doc = parse_file_as_document(&fm, config, &mut errors)?;
if errors.iter().any(is_non_space_after_frameset) {
    log::warn!("text after </frameset> was dropped");
}

Prevention

When it happens

Trigger: Visible text after </frameset>, e.g. `<html><frameset cols="*"><frame src="a.html"></frameset>footer text</html>`. The 'anything else' arm of AfterFrameset mode pushes the error for the Character case.

Common situations: Footers or copyright lines appended to legacy frameset pages; SSI includes adding text at the end of the document; automated appenders writing banners after the frameset.

Related errors

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/15c2f87f487f3fec. Report an issue: GitHub.