Why does firebug add <tbody> to <table>?

To summarize the excellent explanations given in the answers and comments by bobince, Kieron, Alohci and others:

Firebug just displays the DOM of the parsed page. Due to complicated HTML parsing rules, the DOM will "differ" (in some sense) from the source HTML.
In this case the TBODY element in the DOM is added by the HTML parser. Note that this weird parsing is limited to text/html documents and in XHTML the DOM corresponds closely to the source XML.
- This behavior was specified in HTML 4. The content model (allowed children) for table is (CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+) -- trs are only allowed in tbody! The spec says that tbody's start tag is optional, which is supposed to mean that if the HTML parser encounters tr directly inside a table it inserts the tbody start tag omitted by the author.
- To make matters more clear HTML 5 defines very detailed parsing rules, in particular for this case: "When the insertion mode is "in table", tokens must be handled as follows: [...] A start tag whose tag name is one of: "td", "th", "tr" -> Act as if a start tag token with the tag name "tbody" had been seen, then reprocess the current token."

Still,why does it do this?

Mask 2009-11-05 05:18:31

+1 for that but the question is still, why?

NawaMan 2009-11-05 05:18:37

Is not Firefox, but Gecko :P

CMS 2009-11-05 05:23:48

As for "why": Tables are supposed to have a `TBODY`, so Firefox' inner workings *want one to be there*. If you're not specifying it explicitly, it'll create it on its own, because it *wants one to be there*. Even if you're fine eating off the floor, you're placed at a table, because the waiter *wants a table to be there*. ;o)

deceze 2009-11-05 05:42:59

@deceze, that's Firefox deciding that. The W3C standard says no such ting - tbody is optional unless you have a thead or tfoot.

paxdiablo 2009-11-05 06:49:18

@paxdiabolo: This can quickly slide into fine semantics, but: The standard **requires** the use of `TBODY`, **except for** when it's obvious that the only data in the table *is* the `TBODY` (paraphrased, as per your own comment on Kierons answer). That sounds like quite a strong encouragement to me and IMHO may be summarized with "is supposed to be there".

deceze 2009-11-05 09:05:14

If the standard says it doesn't have to be there, it doesn't have to be there. Period. What people or browsers infer is irrelevant. The statement that tables are "supposed to be written with <TBODY>" is clearly incorrect. The standard says it's optional.

paxdiablo 2009-11-05 10:06:02

Obviously the standard can be read both ways. Fact is the *element* exists and *should* be used, but its *declaration can be skipped* if there's no ambiguity. *Internally* the browser just always assumes it's there because it makes implementing it easier. If by "it doesn't have to be there" you mean "its *explicit declaration* can be skipped", then I agree. The *element* though should always implicitly be there, and that's what you're looking at in Firebug. Don't confuse the markup with the interpreted result.

deceze 2009-11-05 11:49:11

The "optional" part is tricky since it depends on the interpretation. You're erring on the side of *skip if not needed*, but the technical easier choice for the browser is *imply if absent*. A Standard™® open to interpretation?! Oh noes, stop the presses! ;o)

deceze 2009-11-05 12:08:20

Great back on forth on standards interpretation. Similar to the perennial: Must <TPAIN> always to be wrapped by <AUTOTUNE>? ;)

micahwittman 2009-12-22 03:59:14

While not the most humorous or witty, this answer is the _correct_ one.

shylent 2009-11-05 05:57:49

This is *not* the correct answer at all. If you're going to link to the standard and then comment on it, you might want to make sure your comment is right. The *standard* states: "TBODY start tag optional, end tag optional" and "The TBODY start tag is always required except when the table contains only one table body and no table head or foot sections. The TBODY end tag may always be safely omitted".

paxdiablo 2009-11-05 06:47:41

That is what “start tag optional” *means*. You can omit the start tag, but an HTML parser must still imply the element is there. The content model of `table` is `(CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)`; note `tr` is *not* in that list. It's like when you forget `<body>`, the parser will imply it as soon as you use an element like `<div>` that must be in body.

bobince 2009-11-05 09:14:12

Note that this case is different for XHTML 1.0, because the weird SGML “start tag optional” feature does not exist in XML (thankfully). In this case the content model includes `(tbody+|tr+)`: you may use tbodies or bare trs but you can't mix them. In served-as-XML parsing mode, Firefox should not add the implied `tbody` element.

bobince 2009-11-05 09:21:53

@bobince, whether the parser implies it or not, the *tag* is optional. The question asked why the tag had appeared.

paxdiablo 2009-11-05 10:04:41

@paxdiablo, right. But then the answer is that firebug doesn't depict *tag*s, it depicts *element*s. The tag is optional, the element is not. (The question now, doesn't use the word "tag" or "element", but it's been edited, so maybe it did originally.)

Alohci 2009-11-05 10:26:58

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Why does firebug add <tbody> to <table>?

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