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This input box has the option to contain one or more filenames in one go:
Single file upload
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For a single filename, click the “Choose file” button, and select the file you want to upload from the file list box appearing - this is pretty much as previous.
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When done, click the Save button to upload your files.
Multiple file upload
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For multiple file upload, the process is almost the same, click the “Choose file” button, but this time select multiple files from the filelist box (by holding down the Ctrl key, you can select individual files) :
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