不，你不能做你想做的事情。你可能不应该尝试。
事实上，你想要一个名为DATA的变量中的一些数据意味着您的POST有效内容（或您的GET查询字符串）将看起来像

 code> DATA = somevar％3Dsomeval％26somevar2％3Dsomeotherval 

如果是它就像

  DATA = somevar = someval& somevar2 = someotherval 
 / pre> 

这意味着：
 

 DATA的值为somevar = someval
 

 somevar2的值为someotherval
 

这是因为每个变量的形式为VARIABLE_NAME = VALUE，并且它们是分开的通过'&'。
 

在你最喜欢的浏览器调试器中检查这个（我使用firebug和chrome内置的开发工具）。 
所以问题是：你为什么要这么做？知道这将更容易帮助您实现您的目标。
 

编辑：示例是错误的
 
I have an HTML form which must be posted to a URL. I would like the form to POST one variable named DATA like so:
DATA: somevar=someval&somevar2=someotherval
I'm having trouble doing this. It seems by default, forms urlencode the data, resulting in:
DATA: somevar%3Dsomeval%26somevar2%3Dsomeotherval
Changing the form's enc-type to "text/plain" results in:
DATA: somevar=someval
SOMEVAR2: someotherval
Is there any way I can have a form actually just send the data as above?
No, you can't do what yo try to do. And you probably shouldn't try.
The fact that you want some data inside a variable called DATA means that your POST payload (or your GET query string) will look like
DATA=somevar%3Dsomeval%26somevar2%3Dsomeotherval
If it was (as you want it to be) like
DATA=somevar=someval&somevar2=someotherval
it would mean:

DATA has a value of 'somevar=someval'

somevar2 has a value of 'someotherval'

This is because each variable has the form VARIABLE_NAME=VALUE, and they are separated by '&'.

Check this yourself in your favourite browser debugger (I use firebug and chrome built-in dev tools).
So, the question is: why are you trying to do this? Knowing that it would be easier to help you achieve your goals.

EDIT: the example was wrong