DevDocs corrections part 1

Started reviewing the developer docs, finding lots of things to correct. I'll do more later, but please review this batch first so I know what, if anything, needs to be fixed moving forward - I'm not entirely sure on the markdownish format used.
My problem is that I'm having a hard time parsing the sentence, so I'm looking for a way to rephrase.  Maybe: "Note: two identical txids cannot be paired together because this would produce the same hash as a single txid being paired with a copy of itself.  Since it is impractical to have separate transactions with identical txids, this does not impose a burden on honest programs but can prevent certain attacks."