Adds Limitations

README.md

@@ -32,6 +32,21 @@ comparison-functions in PHP use. When the first value is smaller than the second
 returns -1, if the first is greater than the second it returns 1 and when both are 
 equals it returns 0. The method can therefore be used as callback to sort arrays.
 
+## Caveat/Limitations
+
+Take care! DateIntervals can be nasty!
+
+Due to their nature DateIntervals do *not* take Date or Time into account! So
+```DateInterval('P1M')``` might or might not be the same as ```DateInterval('P30D')```!
+This Library will compare on a "same entity"-level. So first years are compared, 
+then months, then weeks and so on. Whewn you have an interval that is descibing only 55 weeks
+and compare that to one that is only describing one year, the one year will be considered greater 
+even though 55 weeks are more. So you should only compare comparable intervals! 
+
+The same can happen with f.e. ```new DateInterval('PT36H')``` and ```new DateInterval('P1DT12H')```
+You'd think they are the same, but consider DaylightSavingsTime and they suddenly
+might not be the same! So currently the ```P1DT12H``` would be considered the "higher" one. 
+
 ## License
 
 This library is published under the MIT-License. Find a copy in the LICENSE.md-File.