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+# Hancom-saved fixtures
+
+Documents laid out and saved by Hancom's Hangul. Tests compare what python-hwpx writes, reads or estimates
+with what Hangul stored in them: line layout caches (`hp:linesegarray`), table and object sizes, field and
+style values.
+
+## Saved automatically on Windows
+
+Every file but `equation_*.hwpx` was saved automatically by Hangul's engine for Windows, not from the
+Hangul window on a desktop. Such a save writes `os="2"` in `version.xml` and no `Preview/PrvImage.png`
+(files saved from the desktop program carry `os="1"` and usually a preview image). `memos_in_fields.hwp`
+was saved the same way.
+
+Before a file was committed, only what names its author, the program version and the dates was removed;
+every other part keeps the bytes Hangul wrote.
+
+- `.hwpx`
+  - `version.xml`: `appVersion` emptied.
+  - `Contents/content.hpf`: the `creator`, `lastsaveby`, `CreatedDate`, `ModifiedDate` and `date` metas
+    emptied.
+  - An embedded OLE object (`BinData/*.ole`, a chart): the times of its compound file's root entry zeroed.
+  - The zip repacked with its entries in the same order and compression, dated 1980-01-01 as Hangul
+    dates them.
+- `.hwp`
+  - The summary information stream (`\x05HwpSummaryInformation`): the author, the last saver, the program
+    version, the created and last saved times and the date text emptied. The last printed time is zero as
+    Hangul writes it.
+  - The compound file rebuilt; every other stream is as Hangul saved it.
+
+Their document information therefore differs from that of a file saved from the desktop program, while
+their content and layout caches do not.
+
+## Equations saved on macOS
+
+`equation_*.hwpx` were cut from documents opened and saved by Hangul for macOS (`os="10"` in
+`version.xml`). Each keeps the section's first paragraph and one equation paragraph byte for byte; the
+preview image was left out and the author and dates emptied (#351).
+
+## Adding a file
+
+A file saved from the desktop program works the same: remove the information listed above before
+committing it, and say in the test what behaviour of Hangul the file shows.