code: function handleSuccess(cssText, cssIndex, node, sourceUrl) {
          const returnVal = settings.onSuccess(cssText, node, sourceUrl);
  
          cssText = returnVal !== undefined && Boolean(returnVal) === false ? '' : returnVal || cssText;
  
          resolveImports(cssText, node, sourceUrl, function(resolvedCssText, errorData) {
              if (cssArray[cssIndex] === null) {
                  // Trigger onError for each error item
                  errorData.forEach(data => settings.onError(data.xhr, node, data.url));
  
                  // Filter: Pass
                  if (!settings.filter || settings.filter.test(resolvedCssText)) {
                      cssArray[cssIndex] = resolvedCssText;
                  }
                  // Filter: Fail
                  else {
                      cssArray[cssIndex] = '';
                  }
  
                  handleComplete();
              }
          });
      }
docs: Processes CSS text, updates cssArray, and triggers handleComplete()
  1. Passes CSS to resolveImports
  2. Triggers onError() callback for each @import error
  3. Tests resolved CSS against (optional) RegEx filter
  4. Triggers onSuccess() callback and accepts modified cssText as return
  5. Inserts final CSS into cssArray
  6. Triggers handleComplete() after processing is complete
  
  @param {string} cssText CSS text to be processed
  @param {number} cssIndex cssArray index to store final CSS
  @param {object} node CSS source <link> or <style> node
  @param {string} sourceUrl The URL containing the source node