Open a new, empty workbook (one blank sheet).
Open a new, empty workbook (a readable alias of SpreadsheetEngine.open).
Open a workbook and fill its first sheet from TAB/newline-separated text (each field
inferred as a number, a formula when it begins with =, or text). WebSheets' xlsx
import is JavaScript-driven (the page unzips + parses the XML), so it is not a single
C entry the SDK can wrap; TSV is the curated bulk-load path.
The spreadsheet surface a WebSheets engine module exposes.