The EXTMBR keyword specifies which member of the file is opened. You can specify a member name, '*ALL', or '*FIRST'. Note that '*ALL' and '*FIRST' must be specified in quotes, since they are member "names", not RPG special words. The value can be a literal or a variable. The default is '*FIRST'.
The name must be in the correct case. For example, if you specify EXTMBR(mbrname) and variable mbrname has the value 'mbr1', the member will not be found. Instead, it should have the value 'MBR1'.
If a variable name is used, it must be set before the file is opened. For files that are opened automatically during the initialization part of the cycle, the variable must be set in one of the following ways: