Add start as a modifier in InputFieldSelector

[theGC]

Short description of the issue

start is not available as a modifier within InputFieldSelector

Expected behavior

start to be available

Actual behavior

it isn't

Optional: Screenshots/Links that demonstrate the issue

Optional: Suggestion for a possible fix

Add start modifier to line 588 of wire/modules/Inputfield/InputfieldSelector/InputfieldSelector.module

https://github.com/theGC/processwire/blob/48092d503e90720df796adb0a5f8bfd3afd84889/wire/modules/Inputfield/InputfieldSelector/InputfieldSelector.module#L588

'start' => array(
  'input' => 'integer',
  'label' => $this->_('Start (requires limit)'),
  'operators' => array('=')
),

Steps to reproduce the issue

install processwire, add a selector field to a page

Setup/Environment

any

[theGC]

Also worth adjusting renderTestSelector to allow for the new start modifier:

https://github.com/theGC/processwire/blob/65092e06acd31738122aac95812dfde2b9c9a57f/wire/modules/Inputfield/InputfieldSelector/InputfieldSelector.module#L751

// take into account a limit=n
if(strpos($selector, 'limit=') !== false && preg_match('/\blimit=(\d+)/', $selector, $matches)) {
    $out = ' ' . sprintf($this->_('(%d without limit)'), $cnt);
    // take into account a start=n
    if(strpos($selector, 'start=') !== false && preg_match('/\bstart=(\d+)/', $selector, $startMatches)) {
        $cnt -= $startMatches[1];
        if($cnt < 0) $cnt = 0;
    }
    if($cnt > $matches[1]) $cnt = $matches[1];
}

[ryancramerdesign]

@theGC This one was intentionally left out since it's the current pagination number ($input->pageNum) that determines and sets the start= value. The primary public API usage of it is so that you can specify start=0 to override automatic pagination for things like top level navigation that doesn't change on paginations. I wasn't aware there was a use case for having 'start' in this module. Can you describe more about the use case?

[theGC]

yeah sure, we're using it to allow clients to select pages (categories or products), showing a limited set of these, starting at a certain index.

The above is set up within a matrix repeater, I've screengrabbed a sample set up below:

The above allows the user to create blocks of content, with the same selector broken up over 2 or more parts of the page.