diff --git a/API-Flag.md b/API-Flag.md
index 084dc0a..3fc1018 100644
--- a/API-Flag.md
+++ b/API-Flag.md
@@ -30,6 +30,10 @@ public class YourFlag extends PlotFlag<YourValueType, YourFlag> {
 }
 ```
 
+The flag may implement `com.github.intellectualsites.plotsquared.plot.flags.InternalFlag`, in which case
+the flag won't be visible to the user. This allows you to store information that is 
+associated with the plot, using the flag framework.
+
 The PlotFlag constructor requires three parameters:
 - The (non-null) immutable flag value
 - A flag category