Sorry for asking here. I tried googling it with no luck. I found it in chartjs's core script.
Example(actual code snippet):
// String - Template string for single tooltips
tooltipTemplate: "<%if (label){%><%=label%>: <%}%><%= value %>",
Link: https://github.com/nnnick/Chart.js/blob/master/Chart.js
Do a ctrl+f
for <%
and you will see many of them.
Thanks in advance!