Documentation - Syntax Element

Syntax Element: :

Declares that the symbol on the left hand side inherits from the symbol on the right.

This keyword is highlighted like this.

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// causes version 1.1 to inherit from version 1.0
version 1.1 : 1.0
// causes Y to inherit from X
public table X ("dat_X");
public table Y : X;

Design elements can only inherit from other design elements (not from versions).
Versions can only inherit from other versions (not design elements).
The initialized version may not inherit.
Numbered versions must inherit.
Each version may have at most one inheritor.