example.pp

$foo = 'bar'
$content = template('mymodule/maintemplate.erb')

maintemplate.erb

<% bar = foo + "extra" %>

foobar = scope_function_template(['mymodule/subtemplate.erb'])

subtemplate.erb

<%# here i want to access the variable bar %>
<%= bar %>

there is the function

<%= scope.lookupvar('::bar') %>

is there a kind of parent::bar in erb templateing, or can i pass some variables to the subtemplate, or can i only access the outer variable (of the .pp file) with ::foo