SharePoint provides several tokens that are useful for constructing a context-specific URL.
|~site||Refers to the URL of the current Web site.|
|~sitecollection||Refers to the URL of the parent site collection of the current Web site.|
|~layouts||Refers to _layouts/15 with respect to the Web application.|
|~sitecollectionlayouts||Refers to the layouts folder in thecurrent site collection (such as /sites/mysite/_layouts/15).|
|~sitelayouts||Refers to the layouts folder in the current site (such as site/mysite/mysubsite/_layouts/15)|