Answer true if the stream supports moving backwards with #skip:.
skip: anInteger
Move the position forwards by anInteger places
skipSeparators
Advance the receiver until we find a character that is not a
separator. Answer false if we reach the end of the stream,
else answer true; in this case, sending #next will return the
first non-separator character (possibly the same to which the
stream pointed before #skipSeparators was sent).
skipTo: anObject
Move the current position to after the next occurrence of anObject
and return true if anObject was found. If anObject doesn't exist, the
pointer is atEnd, and false is returned.
skipToAll: aCollection
If there is a sequence of objects remaining in the stream that is
equal to the sequence in aCollection, set the stream position just
past that sequence and answer true. Else, set the stream position
to its end and answer false.