DIALOG-PROCESS AFTER INPUT中的CHAIN

PROCESS AFTER INPUT.
    MODULE EXIT_COMMAND AT EXIT-COMMAND.
    CHAIN. " --屏幕字段遍历处理
          FIELD FIELD1 MODULE MOD1.                "--FIELD1值不为空时都会执行MOD1
          FIELD FIELD2 MODULE MOD2 ON REQUEST.     "--FIELD2值在屏幕中被修改才会执行MOD2
          FIELD FIELD3 MODULE MOD3.                "--FIELD3值不为空时都会执行MOD3
          FIELD: FIELD4, FIELD5 MOD45 ON REQUEST.  "--FIELD4、FIELD4值在屏幕中都被修改才会执行MOD45
    ENDCHAIN.
    MODULE USER_COMMAND.
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屏幕中FIELD2 = xxx,FIELD3 = xxx, 屏幕动作 只修改FILED1的值, 回车或点击其他用户命令(非E)
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若MOD1中: FIELD2 = zzz, FIELD3 = zzz,
执行FIELD FIELD1后FIELD2 = zzz,FIELD3 = zzz,
执行FIELD FIELD2后 不会进入MOD2，但此时FIELD2 = xxx,FIELD = zzz,
(FILED2被修改为PROCESS AFTER OUTPUT后的值，也就是PROCESS AFTER INPUT用户命令动作前的值)
若MOD3中: FIELD2 = yyy,
执行FIELD FIELD3后 最终FIELD2 = yyy, FIELD3 = xxx
(FILED3被修改为PROCESS AFTER OUTPUT后的值，也就是PROCESS AFTER INPUT用户命令动作前的值)
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