Dealing with HTML that has multiple form fields

behat.inc.php

    /**
     * @hidden
     *
     * @Then /^I fill in the form field with id "([^"]*)" number "([^"]*)" with the value of "([^"]*)"$/
     */
    public function fillInTheFormFieldWithIDNumberWithTheValueOf($arg1, $arg2, $arg3)
    {
        $arg = $arg2 - 1; //most users do not start at 0
        $form_field = $this->getMainContext()->getSession()->getPage()->findAll('css', $arg1);
        if($form_field) {
            $form_field[$arg]->setValue($arg3);
        } else {
            throw new Exception('Form Element not found');
        }
    }

Having multiple elements with the same id is invalid HTML. It is better to fix it rather than finding a way to make Behat and Mink accept it IMO

@stof
i think the name of the method is misleading. the "id" is $arg1 and will be used as css selector in the code.
this could be something as simple as "input" and would match any element on the page without violating any HTML rules.