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+# Double Width
+
+The code to decide whether a unicode codepoint should be rendered double-width
+is generated from the Unicode specification.
+This is done by using `tools/unicode_dbl_width.py`.
+
+1. Download <https://www.unicode.org/Public/UCD/latest/ucdxml/ucd.all.flat.zip>
+2. Extract it
+3. Run `tools/unicode_dbl_width.py ucd.all.flat.xml src/bin/termptydbl.h src/bin/termptydbl.c`_
+4. Commit the files modified