mention .invisible in docs per 10102
mention .invisible in docs per 10102

BS3 commits: 2d1fa8cb5bdb61043b1abad5497ce2c74764106e

2947721120/googlebt4,todc/todc-bootstrap,ztx1491/todc-bootstrap,mozillo/todc-bootstrap,up2vs/todc-bootstrap,todc/todc-bootstrap,todc/todc-bootstrap,aaroncnhk/todc-bootstrap,2947721120/todc-bootstrap