Mark a checkbox as checked in a word (.docx) form

I'm using ruby/nokogiri to parse a word form and fill the fields. I've already managed to fill the text fields but I'm having difficulties to check a checkbox. I've looked on the document.xml and didn't notice any different tags when the checkbox is marked or not

How do I tick a checkbox in DOCX?

Click the drop down arrow to view the options and select "Define New Bullet." This will generate a panel of symbol options. Click the box symbol and select "OK" to continue. Now create a bullet list and it will use the checkbox symbol rather than the traditional bullet.

How do I make checkboxes ticked in Word?

On the Home tab, choose the down-arrow next to the Bullets list to open the bullet library, and then choose the checkbox symbol.

I've found the solution when a checkbox is checked, there is a tag: <checked /> and when it isn't checked it is: <checked val='0' />