Function scan_text_segments 

pub fn scan_text_segments(
    text: &str,
) -> Result<Vec<TextToken<'_>>, MarkupScanError>

Scans text for {expr} and [markup] syntax, yielding tokens in order.

Markup rules:

• [identifier] or [identifier key=val …] → TextToken::MarkupOpen
• [/identifier] → TextToken::MarkupClose
• [identifier /] or [identifier key=val … /] → TextToken::MarkupSelfClose
• […] whose content does not match any of the above → emitted verbatim as part of a TextToken::Literal

An unclosed { or [ (no matching } / ] before end of input) is always an error regardless of the content inside.

Errors

Returns MarkupScanError::UnclosedBrace or MarkupScanError::UnclosedBracket with the byte offset of the unmatched delimiter.