Workaround in Sass for EPUB2's XHTML not supporting `start` attribute

start-attribute-workaround.scss

// Workaround for EPUB2's XHTML not supporting `start` attribute
// In HTML, regex search-replace
// <ol (.*?)start="(\d+)"
// with
// <ol \1class="start-\2"

// Create 20 options for starting numbering
@for $i from 2 through 20 {
  $start: $i + 1;
  // If we the list ol to start at 1, the first li will be 2
  // Then to show the new numbering, we set the li to display as a block
  // with a generated number `:before` it that follows the reset numbering
  ol.start-#{$i} {
    counter-reset: start ($i - 1);
    li {
        display: block;
    }
    li:before {
        content: counter(start) ". ";
        counter-increment: start;
    }
    // Nested lists shouldn't keep counting, so 
    // reset the counters and :before content for nested lists
    ol li {
        display: list-item;
        counter-reset: start 1;
    }
    ol.start-3 ol li:before {
        content: normal;
    }
  }
}