Robert Sanderson writes:
 > To go right the way back to the beginning, the original requirement
 > was to be able to say that you want to search for specific
 > locations within a string, for example marc.008 =/substring=1:6
 > 061223
 > 
 > As substring isn't marc specific, (eg both SQL and XPath have a
 > substring function), it was decided it should go into the cql
 > context set.  At which point several different extensions (such as
 > negative numbers for counting backwards) were introduced to make it
 > more featureful.
 > 
 > This isn't covered by existing masking characters, so we do need at
 > least start:length, where both start and length are positive
 > integers.

Yes, of course.  Which is exactly what the proposal said before we all
got sidetracked into inventing new ways to do truncation:

	substring := <start1> [ ':' <length> ]

Where <start1> is a one-based character-count (0 is illegal) and the
:<length> is optional.  If <length> is negative, it counts backwards
from the end of the string.  So:

	1:10 -- First ten characters
	0:10 -- *error*
	1 -- Whole string (from first to end)
	2 -- All of string except the first character

No negative numbers, no special cases.

Agreed?

 _/|_	 ___________________________________________________________________
/o ) \/  Mike Taylor  <[log in to unmask]>  http://www.miketaylor.org.uk
)_v__/\  "No no, no no no no, no no no no, no no; there's no limits" --
	 some bunch of talentless nobodies.