A helper function is a function that is used in an html template. the output of the function gets printed to the template. a helper function can take one or more parameters.
Helper functions are Go html/template concept it’s not introduced by xlog. an example can be found in html/template documentation.
Extensions can define their own helpers to be used by any template using RegisterHelper function. Registering a new helper has to be in the extension init function to be find at the time of parsing the templates.