What is the story behind _SPI_PLAN_MAGIC?

Hi there,

Reading through the SPI code I see this definition:

  #define _SPI_PLAN_MAGIC 569278163

Which is used in he _SPI_plan struct in src/include/executor/spi_priv.h:

  typedef struct _SPI_plan
  {
      int magic;
      ...
  }

What is its purpose?

Thank you.
Marcelo