Ini setting for setting up custom attribute for table summary and caption:

[table]
CustomAttributes[]=summary
CustomAttributes[]=caption

# Example on forcing summary in tables (in OE 5.0)
[CustomAttribute_table_summary]
Required=true

Template code:

<table{if is_set( $summary )} summary="{$summary|wash}"{/if} .....>
{if is_set( $caption )}<caption>{$caption}</caption>{/if}

Files to modify:
ezwebin/override/templates/datatype/ezxmltext/table_cols.tpl
ezwebin/override/templates/datatype/ezxmltext/table_comparison.tpl

design/standard/templates/content/datatype/pdf/ezxmltags/table.tpl (??)
design/standard/templates/content/datatype/view/ezxmltags/table.tpl

Related:
http://issues.ez.no/IssueView.php?Id=10888&activeItem=1
http://issues.ez.no/IssueView.php?Id=5253&activeItem=3
http://www.w3.org/TR/WCAG10-HTML-TECHS/#table-summary-info