Nesting with three levels of quotations

I am trying to create a php variable that has three levels of nested quotes. How do I make a third level around "tackEvent", "downloads", "all", and "nofilter"? The double quotes that I have there are not working.

  $outputList .= "<a href=files/".$content_file ." onClick='_gaq.push
(["_trackEvent", "downloads", "all", "nofilter"])开发者_JS百科;' >" . $content_name . 
"</a>";

From here:

• Outer quote = " (This marks the beginning and end of the string)
• Inner quote = \" (Escaped as to not flag "beginning/end of string")
• Third-tier quote = ' (Literal quote)
• Fourth-tier quote = \' (Literal quote that will be generated as an escaped outer quote)

• Outer quote: "
• Inner quote: '
• Third-tier quote: \"
• Fourth-tier quote: "

$outputList .= <<<LINK
<a href="files/$content_file" onClick="_gaq.push(['_trackEvent', 'downloads', 'all', 'nofilter']);">$content_name</a>
LINK;

This is using heredoc syntax.

From the manual:

To specify a literal single quote, escape it with a backslash (\). To specify a literal backslash, double it (\\).

This applies to strings in double quotes as well.

$str = "I am a string with a quote that says, \"I like quotes\"";