nvim-treesitter/runtime/queries/heex/injections.scm

; directives are standalone tags like '<%= @x %>'
;
; partial_expression_values are elixir code that is part of an expression that
; spans multiple directive nodes, so they must be combined. For example:
;     <%= if true do %>
;       <p>hello, tree-sitter!</p>
;     <% end %>
(directive
  [
    (partial_expression_value)
    (ending_expression_value)
  ] @injection.content
  (#set! injection.language "elixir")
  (#set! injection.include-children)
  (#set! injection.combined))

; Regular expression_values do not need to be combined
((directive
  (expression_value) @injection.content)
  (#set! injection.language "elixir"))

; expressions live within HTML tags, and do not need to be combined
;     <link href={ Routes.static_path(..) } />
(expression
  (expression_value) @injection.content
  (#set! injection.language "elixir"))

; HEEx comments
((comment) @injection.content
  (#set! injection.language "comment"))