Forms with action=""

I usually use

<form method='POST' action='?'>

This means the current URL but with no parameters.

The action attribute is required but you can specify an empty URI reference that referes to the current URI:

<form method="POST" action="">

Edit Ok, this actually is a filed bug of WebKit 528+ (see Bug 19884) when an empty URI is used with a specified base URI using the BASE element. In that case WebKit takes the base URI instead of resolving the empty URI from the base URI.

But this is correct behavior according to RFC 3986:

5.1. Establishing a Base URI

The term "relative" implies that a "base URI" exists against which the relative reference is applied. […]

The base URI of a reference can be established in one of four ways, discussed below in order of precedence. The order of precedence can be thought of in terms of layers, where the innermost defined base URI has the highest precedence. This can be visualized graphically as follows:

  .----------------------------------------------------------.
  |  .----------------------------------------------------.  |
  |  |  .----------------------------------------------.  |  |
  |  |  |  .----------------------------------------.  |  |  |
  |  |  |  |  .----------------------------------.  |  |  |  |
  |  |  |  |  |       <relative-reference>       |  |  |  |  |
  |  |  |  |  `----------------------------------'  |  |  |  |
  |  |  |  | (5.1.1) Base URI embedded in content   |  |  |  |
  |  |  |  `----------------------------------------'  |  |  |
  |  |  | (5.1.2) Base URI of the encapsulating entity |  |  |
  |  |  |         (message, representation, or none)   |  |  |
  |  |  `----------------------------------------------'  |  |
  |  | (5.1.3) URI used to retrieve the entity            |  |
  |  `----------------------------------------------------'  |
  | (5.1.4) Default Base URI (application-dependent)         |
  `----------------------------------------------------------'

In this case the BASE element with href attribute is a base URI embedded in content. And base URI embedded in content has a higher precedence than URI used to retrieve the entity. So WebKit’s behavior is actually the expected behavior according to RFC 3986.

But in HTML 5 this behavior of an empty URI in form’s action (still a draft) differs from RFC 3986:

If action is the empty string, let action be the document's address.

Note: This step is a willful violation of RFC 3986, which would require base URL processing here. This violation is motivated by a desire for compatibility with legacy content. [RFC3986]

Frankly, an HTML comment after this note in the source code reads:

<!-- Don't ask me why. But that's what IE does. It even treats
action="" differently from action=" " or action="#" (the latter
two resolve to the base URL, the first one resolves to the doc
URL). And other browsers concur. It is even required, see e.g.
  http://bugs.webkit.org/show_bug.cgi?id=7763
  https://bugzilla.mozilla.org/show_bug.cgi?id=297761
-->

So this is rather a bug originated from Internet Explorer that became a de-facto standard.

The best way in my opinion would be not to omit the action attribute (which would not validate) but to specify the actual action for the form. Is there a reason you are not specifying the action?

Forms with action=""

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