Filepath

When a parameter accepts a filepath as input, this means either the document name or the full file-path. When you specify only a document name it will be saved in the default folder, usually the one with the data-file.
Each element name (folder or file name) can't be longer than 31 characters. If the filepath contains longer names the name is clipped to 31 characters and thus the folder or file will not be found.
If you specify the full pathname it may contain names of aliases. These aliases are resolved for you, even if they lead to an unmounted file-server volume which is then mounted. You can also use an empty string as the path to let the user select the location of the file to create.
When using System 7.0 or later and a folder can not be found and its length is four characters the code tries to see if it is a special system related folder abbreviation:

These folder types are valid since System 7.0:

Folder type:      Folder Name:                                             
amnu                Apple Menu Items
ctrl                  Control Panels
desk                 Desktop Folder
empt                WhereToEmptyTrash (for network trash)
extn                 Extensions
macs                System Folder
pref                 Preferences
prnt                 PrintMonitor Spool
strt                 Startup Items
temp                Temporary Items
trsh                 Trash

And this folder type is normally installed since System 7.1:

Folder type:     Folder Name:                                             
font                  Fonts

Something like the path below would be a valid filepath, unless one of the elements doesn't exist, or an alias references to a non-existing object, or to a file while a folder is expected:

  Macintosh HD:4D:Second Disk alias:Sound:Female Voice

This one points to the startup folder of the specified ”Macintosh HD“ volume:

  Macintosh HD:strt:Female Voice

And this one to the startup items folder of the current system volume while you don't need to know the volume name (”Macintosh HD“):

  strt:Female Voice

This one would lead to the same location:

  Second Disk:desk:Macintosh HD alias:strt:Female Voice

After the ”Macintosh HD alias“ is resolved you're on the ”Macintosh HD“ volume and the ”strt“ folder becomes the Startup Items Folder on that volume.
But to explain this last example in full: On the ”Second Disk“ volume is in its Desktop Folder (”desk“) an alias present by the name ”Macintosh HD alias“. This alias points to any file or folder on the volume ”Macintosh HD“, but probably to the disk itself. Since we are now on the ”Macintosh HD“ disk the ”strt“ part points to the Startup Items folder on that disk, and that's were the file ”Female voice“ is located (or created).