function ExtractToByte(
    const AIndex: Integer
): Byte;

Byte - Value extracted from the internal storage for the buffer.

ExtractToByte is a Byte function used to read and remove a specified byte value from the internal storage for the buffer. 

AIndex is the zero-based offset of the byte value to extract from the internal storage for the buffer. AIndex normally contains a value in the range 0 (zero) to Size-1. When AIndex contains 0 or a positive value, the content in the buffer is not altered by the Extract operation. 

Using a negative value in AIndex indicates that data is being accessed sequentially and calls Remove to adjust the current buffer position and the space allocated for the buffer. 

ExtractToByte returns a single byte value using the Encoding for the buffer. 

Use one of the other Extract methods to read a specific data type from the internal storage for the buffer: 

Use IndexOf to find the position in the buffer where a specific sequence of byte values is located. 

Use PeekByte to access a specific byte value by its' position in the buffer.