Understanding how to apply validation rules based on specific inputs or booleans in Sanity.io

...

{
  name: 'trigger',
  title: 'Validate',
  type: 'boolean',
},
{
  name: 'email',
  type: 'string',
  title: 'Email',
  validation: Rule => Rule.custom((_, context) => context.document.trigger ? "Email is required" : true)
},

...

validation: Rule => Rule.custom((validate, context) => (context.document.trigger && validate === undefined) ? "Email is required" : true)

{
      name: "title",
      title: "Title",
      description: "Use the correct title",
      type: "string",
      validation: Rule =>
        Rule.custom((title, context) =>
          context.document.deleted && title === undefined
            ? "Title is required"
            : true
        )
    },

    {
      name: "title",
      title: "Title",
      description: "Use the correct title",
      type: "string",
      validation: Rule =>
        Rule.custom((title, context) =>
          context.document.deleted === true && title === undefined
            ? true
            : "Title required"
        )
    },
    {
      name: "deleted",
      title: "Deleted",
      description: "Prevent this variant from being added to the store",
      type: "boolean"
    },

context.document.deleted ? true : "Title required"

 {
      name: "title",
      title: "Title",
      description: "Use the correct title",
      type: "string",
      validation: Rule =>
        Rule.custom((title, context) => {
          const validTitle = title && title !== undefined;
          const isDeleted = context.document.content.main.deleted;
          if (isDeleted && !validTitle) {
            return true;
          } else if (validTitle) {
            return true;
          } else return "Needs a valid title";
        })
    },