Linked parent-child product characteristics ddns

-- url of the page with the problem -- localhost
-- HikaShop version -- :HK Essential: 2.3.0
-- Joomla version -- :2.5.19
-- PHP version -- : 5.3.13
-- Browser(s) name and version -- : FreFox 27.0.1
-- Error-message(debug-mod must be tuned on) -- : Error_message

Hi, I would like to implement linked dynamic comboboxes for product charateristics (ie parent-child drop-downs) using an approach similar to the reference listed below:
Dynamic Dropdowns with charateristics & options

Being a novice HK user, I would like to ask a few questions before venturing in coding:

1. Child drop-down location. My understanding is that the child drop-down html code needs to be explicitely defined. If so, in which file should the child drop-down be inserted into (show_block_characteristics.php, option.php, ..) and how should the select html skeleton be structured? (Note that parents and children share the same class.)

<!-- Parent drop-down skeleton: --> 
<select id="hikashop_product_characteristic_1"  onchange="return hikashopUpdateVariant(this);">.. 
	<option value="10" class="opt1" selected="selected">Option 1</option>
	<option value="11" class="opt2">Option 2</option>
	<option value="12" class="opt3">Option 3</option>
	...
</select>
....
<!-- Child drop-down skeleton: -->
<select id="hikashop_product_option_1" name="hikashop_product_option[1]" onchange="hikashopChangeOption();;">
	<option value="0" class="opt1" selected="selected">None</option>
	<option value="100" class="opt1"> Option 1.1</option>
	...
	<option value="0" class="opt2" selected="selected">None</option>
	<option value="200" class="opt2"> Option 2.1</option>
	....
	<option value="0" class="opt3" selected="selected">None</option>
	<option value="300" class="opt3"> Option 3.1</option>
	...
</select>

// jQuery module:
function hikashopUpdateVariant(elSel) { .... };

Thank you for your explanations.

Meanwhile, I posted a new message about the same topic considering html5 data attributes as a filter option. This would offer better flexibility in case of multiple characteristics drop-downs:
www.hikashop.com/forum/product-category-...in-prod-charact.html