Writing Shopify Bulk Mutation

Question

I am new to GraphQL and new to Shopify. I am having a hard time understanding how to write Bulk operation mutation.

Here is my current challenge.

mutation {
  bulkOperationRunMutation(
    mutation: "mutation call($id: ID!, $input: [PublicationInput!]!) {publishableUnpublish(id: $id, input: $input) { userErrors { message field } } }",
    stagedUploadPath: "'. $uploadFilePath . '") {
    bulkOperation {
      id
      url
      status
    }
    userErrors {
      message
      field
    }
  }
}

I would appreciate if you can help answering the following :

1. What does the keyword call refers to? Is that a GraphQL keyword, or is it an invention by Shopify.

2. How do the argument to call [ in this case $id: ID!, $input: PublicationInput! , relate to argument to actual mutation , in this case id: $id, input: $input

I believe part of the problem is that there are two levels of mutation , on for BulK Operation , and then one for the actual operation , in the case publishableUnpublish.

Hit the following resources with no luck

https://graphql.org/learn/queries/#mutations

https://shopify.dev/docs/api/admin-graphql/2024-01/mutations/publishableUnpublish