diff --git a/ucsinfer/util.py b/ucsinfer/util.py
index 8a3d0ed..fed9e55 100644
--- a/ucsinfer/util.py
+++ b/ucsinfer/util.py
@@ -24,6 +24,9 @@ def ffmpeg_description(path: str) -> Optional[str]:
 
 
 class UcsNameComponents(NamedTuple):
+    """
+    Components of a UCS filename
+    """
     cat_id: str
     user_cat: str | None 
     vendor_cat: str | None
@@ -32,16 +35,57 @@ class UcsNameComponents(NamedTuple):
     source: str | None
     user_data: str | None
 
+    def validate(self):
+        """
+        Check if fields do not contain invalid characters
+        """
+        if not match(r"[A-Z]+[a-z]+", self.cat_id):
+            return False
 
-def parse_ucs(basename: str, catid_list: list[str]) -> Optional[UcsNameComponents]:
+        if self.user_cat and not match(r"[^\-_]+", self.user_cat):
+            return False 
+
+        if self.vendor_cat and not match(r"[^\-_]+", self.vendor_cat):
+            return False
+
+        if not match(r"[^\-_]+", self.fx_name):
+            return False
+
+        if self.creator and not match(r"[^_]+", self.creator):
+            return False 
+
+        if self.source and not match(r"[^_]+", self.source):
+            return False
+
+        if self.user_data and not match(r"[^.]+", self.user_data):
+            return False
+
+
+def build_ucs(components: UcsNameComponents, extension: str) -> str:
+    """
+    Build a UCS filename
+    """
+    assert components.validate(), "UcsNameComponents contains invalid characters"
+
+    return ""
+
+
+def parse_ucs(rootname: str, catid_list: list[str]) -> Optional[UcsNameComponents]:
+    """
+    Parse the UCS components from a file name root.
     
+    :param rootname: filename root, the basename of the file without extension 
+    :param catid_list: a list of all UCS CatIDs
+    :returns: the components, or `None` if the filename is not in UCS format
+    """
+
     regexp1 = r"^(?P<CatID>[A-z]+)(-(?P<UserCat>[^_]+))?_((?P<VendorCat>[^-]+)-)?(?P<FXName>[^_]+)"
 
     regexp2 = r"(_(?P<CreatorID>[^_]+)(_(?P<SourceID>[^_]+)(_(?P<UserData>[^.]+))?)?)?"
     
     regexp = regexp1 + regexp2 
 
-    matches = match(regexp, basename)
+    matches = match(regexp, rootname)
 
     if matches is None:
         return None