Your question is interesting. There will be many approaches. If you want to finely change the search process, it would be to add a new search module. However, it requires advanced skills to do this. I will introduce more simple ways.
Example by layer module (Recommended):
function html() {
if($this->template == 'search') {
if(isset($this->content['q_list']['qs'])) {
foreach($this->content['q_list']['qs'] as $key => $q) {
if(isset($q['raw']['matchparts'])) {
if(substr($q['raw']['matchparts'], 0, 1) != 'Q')
unset($this->content['q_list']['qs'][$key]);
}
}
}
}
qa_html_theme_base::html();
}
Example of core hack: qa-include/qa-app-search.php (around L94 for Q2A V1.6.3)
Before:
// Supplement the results as appropriate
foreach ($results as $key => $result) {
After:
// Supplement the results as appropriate
foreach ($results as $key => $result) {
if (isset($result['match_type'])) {
if($result['match_type'] != 'Q')
$result = null;
}
Other, there will be method to create search index only question.