LOADXX in IPL

When the system is up, operators can type parameters in the system consol, which is connected to the processor. In another way, operators can write the values of the parameters in SYS1.IPLPARM (SYS*.IPLPARM). Those values are stored in members LOADXX. Operators can specify IODF, IEASYM, PARMLIB, SYSCAT, SYSPLEX, etc.
As LOADXX is read, system can know which PARMLIB to use. In a system, operators can specify 10(15?) PARMLIB at most. But system would add SYS1.PARMLIB at the end of the list, so the maximum is 11(16?). If we specify PARMLIB as following:
SYS1.IVAN.PARMLIB     VOL001
SYS1.BACKUP.PARMLIB  VOL002
SYS1.TEST.PARMLIB     SYS500
Then, system would add SYS1.PARMLIB behind SYS1.TEST.PARMLIB, so the list will contain 4 PARMLIB.
If the first one doesn’t exist, the IPL process would look for the next.
LOADXX also specify IEASYM parameters. Using this, systems can know which IEASYM members to use when IPL. Operators can specify more than one IEASYM members by writing there suffixes. IPL process would read them from left to right. If the IEASYM members specified in the right have some duplicated parameters, they would be used by the system and the left ones would be discarded.
After these parameters are specified, system would know what values to be used, which libraries are used and which volumes they reside on. Then IPL process would read these libraries and continue the initialization.