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https://issues.apache.org/jira/browse/DAFFODIL-2692?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17740307#comment-17740307
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Mike Beckerle commented on DAFFODIL-2692:
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Suggest a variant of lengthKind 'pattern' which uses the XSD pattern facet(s) 
should be named lengthKind 'patternFacet'. 

> Add lengthKind 'valuePattern' which uses regex to match allowed data values
> ---------------------------------------------------------------------------
>
>                 Key: DAFFODIL-2692
>                 URL: https://issues.apache.org/jira/browse/DAFFODIL-2692
>             Project: Daffodil
>          Issue Type: New Feature
>          Components: Back End, Front End
>    Affects Versions: 3.3.0
>            Reporter: Mike Beckerle
>            Priority: Major
>
> Existing dfdl:lengthKind 'pattern' uses the pattern to determine the length. 
> No match means length 0.
> People want to use regular expression (or regex) matches differently from 
> this. They want to specify the allowed data patterns, with no match meaning 
> parse error. 
> This should be added as a dfdlx experimental feature to develop experience 
> with it. 
> A few design issues: we need to decide if this pattern includes nil values in 
> its syntax, or if those get added as allowed value patterns automatically. It 
> is simpler if we define this to require that the regex pattern specify all 
> possible data patterns that are accepted, whether they become nilled 
> elements, or elements with values. That, however, requires one to redundantly 
> express the dfdl:nilValue information.
> There may also be an interaction with properties like 
> dfdl:emptyValueDelimiterPolicy and the empty representation. I.e., does the 
> pattern have to allow for a zero-length successful match in order for the 
> data to be zero-length?
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