- * size is significant: its contents are ignored on comparison and output,
- * and unspecified on input.
+ * allocation parameters are significant: its contents are ignored on
+ * comparison and output, and unspecified on input.
+ *
+ * The input format gives the buffer's size, and an optional alignment
+ * specification, in the form %|SZ [`@' M [`+' A]]|%. Each of %|SZ|%, %|M|%
+ * and %|A|% are sizes, as an integer, optionally suffixed with a unit `kB',
+ * `MB', `GB', `TB', `PB', `EB', `ZB', `YB' (with or without the `B')
+ * denoting a power of 1024. The %|SZ|% gives the (effective) buffer size.
+ * %|M|% is the `alignment quantum' and %|A|% is the `alignment offset'; both
+ * default to zero, but if %|M|% is nonzero then the start of the buffer is
+ * aligned such that it is %|A|% more than a multiple of %|M|% bytes. Note
+ * that %|M|% need not be a power of two, though this is common.