Using CALC to set variables inside formatted search

I'm building an application. I want a "create" form, in HTML, that will provide a set of checkboxes.

The items for the checkboxes are in a table in topic "CheckboxItems", e.g.

| *Item* |
| A |
| B |
| C |
| D |
| E |

In my HTML form, I can do this (lines broken for clarity):

%SEARCH{ "^\| +[^\*][^\|]*\|" topic="CheckboxItems" 
  type="regex" multiple="on" nonoise="on" 
  format="<label><input type='checkbox' name='Item' 
    value='$pattern(^\| *(.*?) *\|.*)' class='foswikiCheckbox' 
    /> $pattern(^\| *(.*?) *\|.*) &nbsp;</label>
  "
}%

This works. I see a set of checkboxes in the result.

However, in the interests of DRY (Don't Repeat Yourself), I thought "I'll set a variable for the pattern!"

So, I tried this:

%SEARCH{ "^\| +[^\*][^\|]*\|" topic="CheckboxItems" 
  type="regex" multiple="on" nonoise="on" 
  format="$percntCALC{ $SET(cbitem, $pattern(^\| *(.*?) *\|.*)) 
    <label><input type='checkbox' name='Item' 
    value='$GET(cbitem)' class='foswikiCheckbox' 
    /> $GET(cbitem) &nbsp;</label> }$percnt
  "
}%

I get almost the same output except that it's 'verbatim'. All of the HTML angle brackets are escaped. i.e. the source contains:

&lt;label&gt;&lt;input type='checkbox' name='Item' value='A' class='foswikiCheckbox' /&gt; A &nbsp;&lt;/label&gt;
...

I assume I'm doing something very silly, but what?

-- VickiBrown - 21 Jun 2016

See SpreadSheetPlugin documentation for the SPREADSHEETPLUGIN_ALLOWHTML setting. SSP macros will not emit html, to prevent certain XSS attacks.

-- GeorgeClark - 21 Jun 2016

Here's an approach using FilterPlugin's %FORMATLIST:

%STARTSECTION{"table"}%
| *Item* |
| A |
| B |
| C |
| D |
| E |
%ENDSECTION{"table"}%

%FORMATLIST{
   "$percntINCLUDE{\"%WEB%.%TOPIC%\" section=\"table\"}$percnt"
   split="\n"
   skip="1"
   pattern="\s*\|\s*(.*?)\s*\|"
   format="<label><input type='checkbox' name='Item' value='$1' class='foswikiCheckbox' /> $1</label>"
   separator="$n"
}%

-- Main.MichaelDaum - 21 Jun 2016