Copying lines matching a pattern in VimEdit

My first attempt at this looked like:

:g/something/ normal "Ayy

(ie. for all lines matching "something", append the line to the a register; an uppercase "A" denotes appending to register a and a lowercase "a" would replace the contents of register a)

But it turns out there is a shorter form:

:g/something/y A
:g/something/yank A " alternate form

To inspect the fruits of your labors:

 :registers

Note: if you want to clear the register a you can do qaq (which starts recording a macro into the register and immediately stops recording, leaving the register empty), or:

 :let @a=''