import { createIndentedFilter } from "indented-filter";
const filterFn = createIndentedFilter("x1", (coveredText, attrs) => {
  return customFn(coveredText, attrs)
});
const showdownX1Extension = {
  type: "lang",
  filter: filterFn
};

Example matched cases,

^^x1 hello

^^x1(source="github") hello

![](^^x1(source="github") hello^^)

^^x1(source="github").
  thank you
    very

  much

For more test cases, see /tests/index.spec.yaml

Usage on the browser

<script src="https://unpkg.com/indent-utils@:version/umd/index.min.js"></script>
<script>
const filterFn = createIndentedFilter("x1", (coveredText, attrs) => {
  return customFn(coveredText, attrs)
})
const showdownX1Extension = {
  type: "lang",
  filter: filterFn
}
</script>