[DFDL-WG] Clarification: can you escape a pad char with an escape char?

[Steve Hanson]

Investigation with IBM DFDL using a left justified example...

a) abcd\PPPP gives abcd.
b) abcdP\PPP gives abcdP

...and using a right justified example... 

c) PPP\Pabcd gives Pabcd.
d) PP\PP gives PPabcd

This is asymmetric and is explained by blind trimming of the pad char. 

However it has some merit as it is the simplest rule to devise. Trimming 
is blind to the semantic of any other character and simply removes the pad 
character until it finds another character. To avoid problems don't use 
the same character to both pad and delimit.  Anything else and things 
start to get complicated.

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     dfdl-wg at ogf.org, 
Date:   12/11/2012 23:06
Subject:        [DFDL-WG] Clarification: can you escape a pad char with an 
escape  char?
Sent by:        dfdl-wg-bounces at ogf.org



Did we decide whether an escape character can precede a pad character 
hence, making it part of the content, not the padding?

E.g., suppose pad character is P, escape character is E.

then can 'abcdEPPPP' 

be interpreted as 'abcdP' then 3 pad characters, or did we decide that 
padding ignores escape chars?

I think we decided that padding is outside of the escape blocks, so that 

if [ and ] are my escape block start and end, then PPP[PabcP]PPP would be 
'PabcP' as content. 

but I don't think we commented on regular single escape character 
characters and pad char. 

It seems consistent to me that 'abcdEPPPP' is abcdP as content.

but if not, then 'abcdEPPP' stripping off the trailing padding ends with 
the escape character, so the escape character is escaping nothing hence 
the content would be 'abcd' I believe.

Comments?

...mike

-- 
Mike Beckerle | OGF DFDL WG Co-Chair 
Tel:  781-330-0412
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