The trick is at the beginning of that section: property is an array of criteria, each of which it itself an array/hash with the specified subkeys. So, you don’t set type, text, etc. directly on property, but on a subarray:
property[0][property]=11&property[0][type]=eq&property[text]=teststring
If you’re starting from PHP code, it’s the query string serialization of an array like this:
[
'property' => [
[
'property' => 11,
'type' => 'eq',
'text' => 'teststring',
],
],
]
The “extra” array level is there to allow for multiple queries at once on different (or the same) properties.