All documents subset
The <All Documents> document subset is a special subset that does not behave like the other document subsets in a document set. First of all, this subset is created automatically. In addition, you cannot be set the <All Documents> subset as the default document subset. This is because this is a special subset that does not contain any actual documents, but references that point to the documents in the document subset of the current document set. In addition, you cannot delete the <All Documents> subset.
When the <All Documents> subset is selected, all documents that belong to the document subsets are displayed in one place. These documents are not copied into the <All Documents> subset, there is just a reference that points to the original document subset location for the documents. Because of this behavior, testing or performing a benchmark is simplified. Instead of testing or performing a benchmark for each individual subset separately, you can select the <All Documents> subset and all of the documents in that entire document set.
Also, you are unable to edit the documents displayed when the <All Documents> subset is selected. This is because the documents displayed actually belong to another document subset and are displayed in a read-only format. If you want to edit any of the displayed documents, select the document subset where they are actually located.