Do not attempt to clean the same segment multiple times.

[cumulus.git] / doc / format.txt

diff --git a/doc/format.txt b/doc/format.txt
index 5c9d5fa..5072981 100644 (file)
--- a/doc/format.txt
+++ b/doc/format.txt
@@ -116,12 +116,28 @@ is invalid to select using the slice syntax a range of bytes that does
 not fall within the original object.  The slice specification should be
 appended to an object name, for example:
     a704eeae-97f2-4f30-91a4-d4473956366b/000001ad[264+1000]
-selects only bytes 264..1263 from the original object.
+selects only bytes 264..1263 from the original object.  As an
+abbreviation, the slice syntax
+    [<length>]
+is shorthand for
+    [0+<length>]
 
 Both a checksum and a slice can be used.  In this case, the checksum is
 given first, followed by the slice.  The checksum is computed over the
 original object contents, before slicing.
 
+Special Objects
+---------------
+
+In addition to the standard syntax for objects described above, the
+special name "zero" may be used instead of segment/sequence number.
+This represents an object consisting entirely of zeroes.  The zero
+object must have a slice specification appended to indicate the size of
+the object.  For example
+    zero[1024]
+represents a block consisting of 1024 null bytes.  A checksum should not
+be given.  The slice syntax should use the abbreviated length-only form.
+
 
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