Fossil

always readable and writable.  This can be expressed by "w" permission
if desired but is optional.
The optional 4th argument is the name of the same file as it existed in
the parent check-in.  If the name of the file is unchanged from its
parent, then the 4th argument is omitted.
</p>

<p>
A manifest has zero or more N-cards.  Each N card records a name changes
to one of the files in the manifest.  The first argument to the N code is
the name of the file in the parent check-in.  The second argument is the
name of the file in the check-in defined by the manifest.
</p>

<p>
A manifest has zero or one P-cards.  Most manifests have one P-card.
The P-card has a varying number of arguments that
defines other manifests from which the current manifest
is derived.  Each argument is an 40-character lowercase 
hexadecimal SHA1 of the predecessor manifest.  All arguments
to the P-card must be unique to that line.