A standard procedure call can use any sequence of instructions that present the called routine with the required environment. Although this is true, it is believed that the vast majority of standard conforming external calls will be done with a common sequence of instructions and conventions. This common set of call conventions is so pervasive that it is included for reference as part of this standard.
One important feature of the calling standard is that it is designed such that the same instruction sequence can be used to call each of the different types of procedure. That is, the caller does not have to know which type of procedure is being called.