Selection Surrogate Boundary Check
Check selection endpoints for splitting a UTF-16 surrogate pair; does not guarantee grapheme-cluster boundaries.
Description
Check selection endpoints for splitting a UTF-16 surrogate pair; does not guarantee grapheme-cluster boundaries.
UTF-16 represents some Unicode characters with two code units. A selection boundary between those units can split a surrogate pair even when its numeric offset is in range.
When to use this tool
Check selection endpoints for splitting a UTF-16 surrogate pair; does not guarantee grapheme-cluster boundaries.
- Prepare the supplied text, start, end fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter text, start, end. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.startSplitsSurrogate, result.endSplitsSurrogate. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Validate the half-open start/end span. At each boundary, check whether the preceding unit is a high surrogate and the following unit is a low surrogate, then return the two split flags.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| text | text. | Text; at most 8,192 UTF-16 code units, subject to the grammar above |
| start | start. | Finite number |
| end | end. | Finite number |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.startSplitsSurrogate | Flag for start splits surrogate under the exact condition described above. |
| result.endSplitsSurrogate | Flag for end splits surrogate under the exact condition described above. |
{
"input": {
"text": "\ud83d\ude00",
"start": 1,
"end": 2
},
"output": {
"result": {
"startSplitsSurrogate": true,
"endSplitsSurrogate": false
}
}
}Limitations and assumptions
- This screens surrogate-pair boundaries only. It does not establish grapheme-cluster boundaries or validate every character in the text; combining sequences can remain split without triggering a flag.
- Text offsets and lengths use UTF-16 code units unless explicitly described as bytes or code points. CRLF, CR and LF are recognized as line endings; a terminal newline creates a final empty line in the shared line model.
- Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
- Ordinary string lists have at most 128 entries of at most 128 code units each; numeric lists and matrices have separate bounded size checks. Nonfinite results and excessively large serialized outputs are rejected.
- Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.
Alternative or Complementary methods
Use a parser or language-aware editor when quoting, syntax or nested constructs matter. For plain text transforms, keep UTF-16 offsets, Unicode code points, grapheme clusters and UTF-8 byte offsets distinct; apply changes to the same source version used to calculate spans.
References
Similar or alternative tools
- Selection Indent Transform
Transform full lines intersecting a half-open UTF-16 selection, preserving line endings.
- Selection Outdent Transform
Transform full lines intersecting a half-open UTF-16 selection, preserving line endings.