Searching for keywords in HTML

The iOS app I'm开发者_Go百科 writing displays an HTML page, and I would like to add a search feature where the user can search for instances of a keyword and highlight them.

What's the best way to do this?

NSString *filePath = PATH_OF_HTML_FILE;
NSError *err = nil;
NSString *pageHTML = [NSString stringWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:&err];

if(err)
{
    pageHTML = [NSString stringWithContentsOfFile:filePath encoding:NSASCIIStringEncoding error:&err];

}


if([searchTxtField.text length])
{
    NSRange range1 = [pageHTML rangeOfString:searchTxtField.text options:NSCaseInsensitiveSearch];
    if(range1.location != NSNotFound)
    {
        NSString *highlightedString = [pageHTML substringWithRange:range1]; 
        pageHTML = [pageHTML stringByReplacingOccurrencesOfString:highlightedString withString:[NSString stringWithFormat:@"<span style=\"background-color:yellow; color:red;\">%@</span>",highlightedString] options:NSCaseInsensitiveSearch range:NSMakeRange(0, [pageHTML length]) ];
        [webView loadHTMLString:pageHTML baseURL:[NSURL fileURLWithPath:filePath]];
    }


}