gatsby-config.js settings to generate autolinked headers in MDX files

autolink-headers-in-gatsby-mdx-files

// this is a blend of settings found in two locations in GastbyJS documentation
// gatsby-remark-plugins section in MDX plugins page:
// https://www.gatsbyjs.org/docs/mdx/plugins/#gatsby-remark-plugins
// and gatsby-remark-autolink-headers page options section:
// https://www.gatsbyjs.org/packages/gatsby-remark-auto-headers/?=autolink%20headers#options

module.exports = {
	plugins: [
		'gatsby-remark-autolink-headers',
		{
			resolve: 'gatsby-plugin-mdx',
			options: {
				extensions: ['.mdx', '.md'],
				defaultLayouts: {
					default: require.resolve('./src/templates/docs.js')
				},
				gatsbyRemarkPlugins: [
					{
						resolve: 'gatsby-remark-autolink-headers',
						options: {
							offsetY: `100`,
							icon: `<svg aria-hidden="true" height="20" version="1.1" viewBox="0 0 16 16" width="20"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg>`,
							className: `custom-class`,
							maintainCase: true,
							id: `data-id`
						}
					}
				]
			}
		},
		{
			resolve: 'gatsby-plugin-page-creator',
			options: {
				path: `${__dirname}/src/pages`
			}
		},
	]
};