Conditional "marking" in Rebol / Red parse

Question

Subsequent to Rebol / Red Parse html rules returns true but nothing is inserted

How to mark the end of the fist main div only (when div-count is 0 first time), not the second one, or is there a way to break out of parse conditionally to a variable value ?

        content: {<div class="main">
          <h1>
            Big TITLE
          </h1>
          <div>
            <section>
              <p>a paragraph</p>
            </section>
             <section>
              <p>a paragraph</p>
            </section>
              <section>
              <p>a paragraph</p>
            </section>
           </div>
           <div>
              <p>Blah Blah</p>
           </div>
        </div>
        <div>
          Another Div
        </div>

    <div class="main">
          <h1>
            Big TITLE
          </h1>
          <div>
            <section>
              <p>a paragraph</p>
            </section>
             <section>
              <p>a paragraph</p>
            </section>
              <section>
              <p>a paragraph</p>
            </section>
           </div>
           <div>
              <p>Blah Blah</p>
           </div>

        </div>
        <div>
          Another Div
        </div>    
        }

        rules: [
             thru <div class="main">
             (div-count: 1)
              some [
                "<div" (probe ++ div-count) skip
              |
                "</div>" mark:  ( probe -- div-count   if div-count = 0 [insert mark "closing main div"]) skip 
              |  skip
             ]
          ]
        parse/all content rules 

Answer 1

Here a solution working in Red and Rebol using your approach plus adding some selfmodification to the rules

rules: [
    thru <div class="main">
    (div-count: 1 clear rules/5/8 )
    some [
        "<div" (probe div-count: div-count + 1) skip
        |
        "</div>" mark:  ( 
             probe div-count: div-count - 1   
             if div-count = 0 [
                 insert mark "closing main div"  append rules/5/8 [to end]  
             ]
         ) [] skip 
         |  skip
     ]
 ]

Answer 2

It seems that you need a mix of opt and if keywords. Consider a simplified example:

count: 0
div: ['div some integer! /div]

probe parse [
    div 1 2 3 /div 
    div 4 5 6 /div
    div 7 8 9 /div
][
    some [
        div (count: count + 1) opt [if (count = 1) mark:]
    ] 
]

probe mark

Here, after each div rule match, increment of a counter happens. After that there's an optional match -- if counter is at 1, then current input position is marked, otherwise parsing continues as-is. Because this rule is optional, parsing will continue despite its success or failure.

Additionally, if you want to break out of a parsing loop (that is, some, any or while), you can use break (returns success) or reject (returns failure), again in combination with opt, if and conditional paren! expression.