An interesting case of using the same name: input elements of type checkbox like this:
<input id="fruit-1" type="checkbox" value="apple" name="myfruit[]">
<input id="fruit-2" type="checkbox" value="orange" name="myfruit[]">
At least if the response is processed by PHP, if you check both boxes, your POST data will show:
$myfruit[0] == 'apple' && $myfruit[1] == 'orange'
I don't know if that sort of array construction would happen with other server-side languages, or if the value of the name attribute is only treated as a string of characters, and it's a fluke of PHP syntax that a 0-based array gets built based on the order of the data in the POST response, which is just:
myfruit[] apple
myfruit[] orange
Can't do that kind of trick with ids. A couple of answers in What are valid values for the id attribute in HTML? appear to quote the spec for HTML 4 (though they don't give a citation):
ID and NAME tokens must begin with a letter ([A-Za-z]) and may be
followed by any number of letters, digits ([0-9]), hyphens ("-"),
underscores ("_"), colons (":"), and periods (".").
So the characters [ and ] are not valid in either ids or names in HTML4 (they would be okay in HTML5). But as with so many things html, just because it's not valid doesn't mean it won't work or isn't extremely useful.
