Templating engine supports calling functions like {{ len .Tweet }} where len is a function that returns length of an array or slice.

and, or, not

and, or, not are for logical operations:

https://codeeval.dev/gist/4f9259953079361d8669061bf128ed6e

index

index is for accessing elements of a slice by index or values in a map by key.

https://codeeval.dev/gist/dc5f47467b77c7c8584bd2461ba080fe

len

len returns length of an array of map.

https://codeeval.dev/gist/904b8bed0754de3c10f494930a4a3a83

print, printf, println

print is like fmt.Sprint.

printf is like fmt.Sprintf.

println is like fmt.Sprintln.

https://codeeval.dev/gist/e543f880ba15c189c2e2001c4323ca94

js, html, urlquery

js, html and urlquery is for escaping text so that it can be safely inserted in a JavaScript, HTML and URL context:

https://codeeval.dev/gist/c6e848d05fce4eff392456c83bc87bfc