+: Field Continuation is Not Supported

[seisiuneer]

Report from a user of my tool:

Field continuation lines (https://abcnotation.com/wiki/abc:standard:v2.1#field_continuation) are not supported correctly in rendering the tune. The '+' is interpreted as a bow downstroke (? it's a 'V'). A leading space is interpreted as a trill ('tr'). Valid abc notes (a-gA-G) seem to be interpreted as notes, though not if it occurs as the first letter in the continuation??

Minimal example:

X:1
N:A note
+: continued
ABcdefg ||

[seisiuneer]

Here's a fix that works but is a bit inelegant.

It takes advantage of the behavior that when rendering strings, multiple spaces get collapsed.

It inserts additional spaces to replace the :+ tag and return to keep the offsets correct.

At the top of:

this.parse = function (strTune, switches, startPos)

add this call:

strTune = mergeContinuationLines(strTune);

where mergeContinuationLines( ) is:

  // Find and merge any continuation lines after a tag, but keep the character count the same
  function mergeContinuationLines(text) {
    const lines = text.split(/\r?\n/);
    const out = [];
    let i = 0;

    const baseRe = /^[A-Za-z]:/;   // F: ...   (no capture needed)
    const plusRe = /^\+:(.*)$/;    // +: ...  (capture EVERYTHING after +:)

    while (i < lines.length) {
      const line = lines[i];

      if (baseRe.test(line)) {
        let merged = line;
        let j = i + 1;

        // Collect all +: lines (preserve exact spacing)
        while (j < lines.length) {
          const m = lines[j].match(plusRe);
          if (!m) break;

          const raw = m[1]; // exact text INCLUDING leading spaces
          merged += "   " + raw;  // always prepend 3 spaces
          j++;
        }

        out.push(merged);
        i = j;
      } else {
        out.push(line);
        i++;
      }
    }

    return out.join("\n");
  }

With this in place, the example in the original report renders correctly and has the correct character offsets for notation highlighting: