Improving schema setup for adding bold and italics to a title/string field in Slack thread.

{
      name: 'headingBlock',
      title: 'Hero Title block',
      // fieldset: 'hero',
      of: [
        {
          type: 'block',
          styles: [{title: 'Normal', value: 'normal'}],
          lists: [],
          marks: {
            decorators: [
              {title: 'Strong', value: 'strong'},
              {title: 'Emphasis', value: 'em'},
            ],
          },
        },
      ],
      type: 'array',
      validation: (Rule) =>
        Rule.custom((value, {document}) => {
          if (value && value?.length > 1) {
            return 'This is a title and so can only be one line.';
          }
          return true;
        }),
    },