How Can I Mirror Object: SELECTION?

How can I Mirror Object: SELECTION?

Application of the modifier appears to be limited to just those objects in the pull down list - or have I missed something else that would permit the mirroring of only a selection?

Don’t understand the question ?
Do you mean selection of vertices, objects ?. Objects in the modifier pull down list are to set mirror axis, what else do you want to do with them.
Can you show an image to clearly show what you have and what you are wanting to achieve.

To mirror without the modifier you have the Object / Mirror menu (Ctrl+M)

Thanks Richard. I apologize for not understanding my own question well enough to articulate it.

I’m following a tutorial which used the Modifier, Mirror. I incorrectly tried to apply that method (concept) on a portion (selection of vertices) within the object. Your handy link helps to make clear the distinction between mirroring (objects AND mesh selections) versus using the Modifier, Mirror.

The one (minor) side question which arises: Is there a means to enable duplication of the selection at the same time as it’s being mirrored, much like what happens when using the Modifier, Mirror or must the duplication be done as a separate step prior to mirroring?