Answer to question http://www.question2answer.org/qa/39385/how-can-i-override-qa_post_html_fields-in-qa-app-format-php

qa-theme.php

function doctype(){
	if ($this->template === 'question' && isset($this->content['q_view'])) {
		$this->addCategoryPrefixToTitleInList($this->content['q_view'], isset($this->content['title']));
	}
	qa_html_theme_base::doctype();
}

function addCategoryPrefixToTitleInList(&$q_item, $shouldChangeTitle) {
	if (isset($q_item['raw']['categoryid'], $q_item['raw']['categoryname'], $q_item['title'])) {
		$categoryId = $q_item['raw']['categoryid'];
		if (!empty($categoryId)) {
			$html = sprintf(
				'<span class="qa-q-item-title-cat-%d">%s</span>',
				$q_item['raw']['categoryid'],
				$q_item['raw']['categoryname']
			);
			$q_item['title'] = $html . $q_item['title'];
			if ($shouldChangeTitle) {
				$this->content['title'] = $html . $this->content['title'];
			}
		}
	}
}

function q_item_title($q_item) {
	$this->addCategoryPrefixToTitleInList($q_item, false);
	qa_html_theme_base::q_item_title($q_item);
}