hold Ctrl or equivalent for multiple-selection in the document list
may want a checkbox next to each document that could be used to easily toggle each document to be included or excluded from the phrase list
order of documents is alphabetical including path
this should be the default order that the documents are displayed in the document list
all phrases for the first document are shown in their natural order, followed by all phrases in the second document in their natural order, and so on.
there should be a visual indication of where one document ends and the next begins (design needed)
this could be on the edge of the document list panel, showing a vertical bar for each document that begins at the first and ends at the last phrase in that document.
large documents would have 1 bar with the document name most of the time
small documents would have multiple bars. Single-string documents are the main use-case for multiple document selection, so this is a very relevant case.
all filtering should work as it would for a single document
Note document could just be added as another filtering field, which would potentially allow wildcard searches on document name/path. This is probably out of scope for this task.