https://www.knowledgewalls.com/venkatesan/books/html-4/optgroup
OPTGROUP in FORM ELEMENTS of HTML 4
A-Z HTML 4 tags and attribute explained with examples and output. Easy to learn in the simple way with HTML 4. Contains header, text block, table, form...
in formoptgroupelementshtml
https://www.optgroup.ro/contul-meu/
Contul meu - OptGroup
contul meuoptgroup