Make attribute name and labels more strict

data/schema/SCHEMA-SCHEMA

@@ -10,6 +10,8 @@ key:                mnt-by   required  multiple    lookup=dn42.mntner > [mntner]
 key:                remarks  optional  multiple  > [text]...
 mnt-by:             DN42-MNT
 remarks:            # option descriptions
+                    Attribute names must match /[a-zA-Z]([a-zA-Z0-9_\-]*[a-zA-Z0-9])?/.
++
                     required
                     :    object required to have at least one
                     optional
@@ -38,12 +40,12 @@ remarks:            # option descriptions
                     * must come last in option list
 +
                     [label] string value. A positional string argument required.
-                    Text inside brackets represent a label for the string.
+                    Text inside brackets represent a label for the string and must match the same rules as attribute names.
                     If follwed by '...' values are gathered as an array.
 +
                     {enum1|enum2|} enumeration. One option in pipe('|') deliniation is allowed.
-                    If there is a trailing pipe it means the enum is optional.
+                    If there is a trailing pipe it means the enum is optional. Enum values must match the same rules as attribute names.
 +
-                    label=str keyword argument. Label for value with type 'str', 'int', or 'decimal'
+                    label=str keyword argument. Label for value with type 'str', 'int', or 'decimal'. The label must match the same rules as attribute names.
 +
-                    'literal' Literal value. literal text value.
+                    'literal' Literal value. literal text value which must not contain any whitespace or single quotes.