https://docwiki.embarcadero.com/RADStudio/Alexandria/en/What%27s_New#Binary_Literals_and_Digit_Separator tells us: The language also introduces a digit separator that can be used to improve the readability of literal values with many digits. The separator is the underscore “_” and it is basically ignored when parsing and compiling the code. This is very similar to the feature introduced in C# 7.0. ``` const AMillion = 1_000_000; ``` Of course, you can use the digit separators for binary literals. FPC 3.2.3 don't support it. Test file: ``` 1_2 1_2.3_4e+5_6 1_2._3_4e+_5_6 //is it ok? $A_B $_A_B //is it ok? %1_0 %_1_0 //is it ok? &7_0 &_7_0 //is it ok? ```