In telecommunications, a self-synchronizing code, or comma-free code, is a line code that can be easily synchronized. Such line codes have the property that the code which is made of a part of the code word, or two overlapping code words is not a valid code. An example, take the code words "11" and "00", and the code "11 00 00 11 00". The spaces have been added to show the different words, and are not really in the code. Let's now assume that four letters (two code words) are read. The code "1000" is not a valid code, because "10" is not one of the two code words defined. Similarly, "0001". Even though "00" is a valid word, "01" is not. The only valid way to read two valid words from the example given is by starting at the very beginning, or just after one of the spaces, which have been inserted for clarity only.