what does AT do in a linker scripts ?

[Yubin Ruan]

Hi,
I am reading some C code and some linker scripts for `ld`.
I find something really hard to understand:

     .text : AT(0x100000) {
         *(.text .stub .text.* .gnu.linkonce.t.*)
     }

I understand what the `.text` and the wild char * do, but what does the 
`AT` after the colon do ?
Need help.
And also, why is there no man page describing the syntax of linker scripts ?

Regards,
Ruan