how to extract meta keywords value from a webpage?

Merged with unable to extract meta keyword value from website using get_meta_tags() .

$all_meta=get_meta_tags($website_name);
$keyword_meta=$all_meta['keywords'];
print_r($all_meta);

print_r($all_meta) only returns开发者_Go百科 keywords from web page containing exactly the word 'keywords'...But few web-pages contain meta information in 'Keywords'...Can u tell me how to extract keywords which is independent of case?

take case of website-"http://www.microsoft.com"

$all_meta=get_meta_tags("www.microsoft.com"); $keyword_meta=$all_meta['Keywords'];
$keyword_meta1=$all_meta['keywords'];

print_r($keyword_meta); //shows error

print_r($keyword_meta1); /*displays Microsoft, product, support, help, *training, Office, Windows, software, download, trial, preview, demo, business, security, *update, free, computer, PC, server, search, download, install, news */

so how to make it run for case-insensitive keys-'keywords' or 'Keywords' ??