Explore ExtractConfig request syntax on custom forms

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>

2 files changed, 493 insertions, 0 deletions

diff --git a/Lessons_uncategorized/Lesson_Configuration_Language_4/README.md b/Lessons_uncategorized/Lesson_Configuration_Language_4/README.md
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+Now let's try to dump the configuration settings for the applications that we've created earlier.
+
+# `HIIFormCheckbox.efi`
+
+Let's take `HIIFormCheckbox.efi` as initial example. This is our minimal HII Form application.
+
+Load its driver in UEFI shell:
+```
+FS0:\> load HIIFormCheckbox.efi
+```
+And check `HIIConfig.efi dump` output:
+```
+FS0:\> HIIConfig.efi dump
+<...>
+```
+It can be a surprise, but the `EFI_HII_CONFIG_ROUTING_PROTOCOL.ExportConfig()` call doesn't return settings for the storage created by the `HIIFormCheckbox.efi` driver. But at the same time it is possible to return this settings via the direct `EFI_HII_CONFIG_ROUTING_PROTOCOL.ExtractConfig()` call. This is the behaviour for storages created with a help of a `efivarstore` helper.
+
+So let's try to construct request for our storage. This is the example from the `UefiLessonsPkg/HIIFormCheckbox/Form.vfr` code:
+```
+#define FORMSET_GUID  {0xef2acc91, 0x7b50, 0x4ab9, {0xab, 0x67, 0x2b, 0x4, 0xf8, 0xbc, 0x13, 0x5e}}
+
+formset
+  guid     = FORMSET_GUID,
+  title    = STRING_TOKEN(FORMSET_TITLE),
+  help     = STRING_TOKEN(FORMSET_HELP),
+
+  efivarstore UINT8,
+    attribute = EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_NON_VOLATILE,
+    name  = CheckboxValue,
+    guid  = FORMSET_GUID;
+
+  form
+    formid = 1,
+    title = STRING_TOKEN(FORMID1_TITLE);
+
+    checkbox
+      varid = CheckboxValue,
+      prompt = STRING_TOKEN(CHECKBOX_PROMPT),
+      help = STRING_TOKEN(CHECKBOX_HELP),
+    endcheckbox;
+  endform;
+endformset;
+```
+And here is how we encoded DevicePath in the `UefiLessonsPkg/HIIFormCheckbox/HIIFormCheckbox.c` file:
+```
+HII_VENDOR_DEVICE_PATH  mHiiVendorDevicePath = {
+  {
+    {
+      HARDWARE_DEVICE_PATH,
+      HW_VENDOR_DP,
+      {
+        (UINT8) (sizeof (VENDOR_DEVICE_PATH)),
+        (UINT8) ((sizeof (VENDOR_DEVICE_PATH)) >> 8)
+      }
+    },
+    FORMSET_GUID
+  },
+  {
+    END_DEVICE_PATH_TYPE,
+    END_ENTIRE_DEVICE_PATH_SUBTYPE,
+    {
+      (UINT8) (END_DEVICE_PATH_LENGTH),
+      (UINT8) ((END_DEVICE_PATH_LENGTH) >> 8)
+    }
+  }
+};
+```
+
+Putting all of this together our request would look like this:
+```
+HIIConfig.efi extract ef2acc91-7b50-4ab9-ab67-2b04f8bc135e CheckboxValue VenHw(ef2acc91-7b50-4ab9-ab67-2b04f8bc135e)
+```
+
+So let's try to use it:
+```
+FS0:\> HIIConfig.efi extract ef2acc91-7b50-4ab9-ab67-2b04f8bc135e CheckboxValue VenHw(ef2acc91-7b50-4ab9-ab67-2b04f8bc135e)
+
+Request: GUID=91cc2aef507bb94aab672b04f8bc135e&NAME=0043006800650063006b0062006f007800560061006c00750065&PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400
+Response: GUID=91cc2aef507bb94aab672b04f8bc135e&NAME=0043006800650063006b0062006f007800560061006c00750065&PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400&OFFSET=0000&WIDTH=0001&VALUE=00&GUID=91cc2aef507bb94aab672b04f8bc135e&NAME=0043006800650063006b0062006f007800560061006c00750065&PATH=0104140091cc2aef507bb94aab672b0<...>
+
+
+GUID=91cc2aef507bb94aab672b04f8bc135e (EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E)
+NAME=0043006800650063006b0062006f007800560061006c00750065 (CheckboxValue)
+PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400 (VenHw(EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E))
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+
+GUID=91cc2aef507bb94aab672b04f8bc135e (EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E)
+NAME=0043006800650063006b0062006f007800560061006c00750065 (CheckboxValue)
+PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400 (VenHw(EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E))
+ALTCFG=0000
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+
+GUID=91cc2aef507bb94aab672b04f8bc135e (EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E)
+NAME=0043006800650063006b0062006f007800560061006c00750065 (CheckboxValue)
+PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400 (VenHw(EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E))
+ALTCFG=0001
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+```
+
+The output is broken in 3 groups. The first group corresponds to the current data setting. Currently the UINT8 value for the Checkbox is equal to 0x00.
+
+The next 2 groups describe alternative configurations. These configurations under the `ALTCFG=0000` and `ALTCFG=0001` correspond to defaults:
+- `ALTCFG=0000` - Standard default
+- `ALTCFG=0001` - Manufacturing default
+
+We don't have any code for the defaults in our VFR, therefore HII subsystem have returned zero values in them.
+
+Now let's try to go to the form browser and manually change the checkbox value.
+
+After that issue the extract call again:
+```
+FS0:\> HIIConfig.efi extract ef2acc91-7b50-4ab9-ab67-2b04f8bc135e CheckboxValue VenHw(ef2acc91-7b50-4ab9-ab67-2b04f8bc135e)
+
+Request: GUID=91cc2aef507bb94aab672b04f8bc135e&NAME=0043006800650063006b0062006f007800560061006c00750065&PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400
+Response: GUID=91cc2aef507bb94aab672b04f8bc135e&NAME=0043006800650063006b0062006f007800560061006c00750065&PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400&OFFSET=0000&WIDTH=0001&VALUE=01&GUID=91cc2aef507bb94aab672b04f8bc135e&NAME=0043006800650063006b0062006f007800560061006c00750065&PATH=0104140091cc2aef507bb94aab672b0<...>
+
+
+GUID=91cc2aef507bb94aab672b04f8bc135e (EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E)
+NAME=0043006800650063006b0062006f007800560061006c00750065 (CheckboxValue)
+PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400 (VenHw(EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E))
+OFFSET=0000  WIDTH=0001  VALUE=01
+01                                               | .
+
+GUID=91cc2aef507bb94aab672b04f8bc135e (EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E)
+NAME=0043006800650063006b0062006f007800560061006c00750065 (CheckboxValue)
+PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400 (VenHw(EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E))
+ALTCFG=0000
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+
+GUID=91cc2aef507bb94aab672b04f8bc135e (EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E)
+NAME=0043006800650063006b0062006f007800560061006c00750065 (CheckboxValue)
+PATH=0104140091cc2aef507bb94aab672b04f8bc135e7fff0400 (VenHw(EF2ACC91-7B50-4AB9-AB67-2B04F8BC135E))
+ALTCFG=0001
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+```
+
+You can see how the returned data in the first group (current setting) has changed to the 0x01.
+
+# `HIIFormDataElements.efi`
+
+Now let's try to work with more advanced application: `HIIFormDataElements.efi`.
+
+It encodes data in a custom `UEFI_VARIABLE_STRUCTURE` (`UefiLessonsPkg/HIIFormDataElements/Data.h`):
+```
+#define FORMSET_GUID  {0x531bc507, 0x9191, 0x4fa2, {0x94, 0x46, 0xb8, 0x44, 0xe3, 0x5d, 0xd1, 0x2a}}
+
+#define UEFI_VARIABLE_STRUCTURE_NAME L"FormData"
+
+#pragma pack(1)
+typedef struct {
+  UINT8 CheckboxValue;
+  UINT16 NumericValue;
+  CHAR16 StringValue[11];
+  EFI_HII_DATE DateValue;
+  EFI_HII_TIME TimeValue;
+  UINT8 OneOfValue;
+  UINT8 OrderedListValue[3];
+} UEFI_VARIABLE_STRUCTURE;
+#pragma pack()
+```
+
+And the VFR code looks like this (`UefiLessonsPkg/HIIFormDataElements/Form.vfr`):
+```
+formset
+  guid     = FORMSET_GUID,
+  title    = STRING_TOKEN(FORMSET_TITLE),
+  help     = STRING_TOKEN(FORMSET_HELP),
+
+  efivarstore UEFI_VARIABLE_STRUCTURE,
+    attribute = EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_NON_VOLATILE,
+    name  = FormData,
+    guid  = FORMSET_GUID;
+
+  defaultstore StandardDefault,
+    prompt      = STRING_TOKEN(STANDARD_DEFAULT_PROMPT),
+    attribute   = 0x0000;
+
+  defaultstore ManufactureDefault,
+    prompt      = STRING_TOKEN(MFG_DEFAULT_PROMPT),
+    attribute   = 0x0001;
+
+  form
+    formid = 1,
+    title = STRING_TOKEN(FORMID1_TITLE);
+
+    checkbox
+      varid = FormData.CheckboxValue,
+      prompt = STRING_TOKEN(CHECKBOX_PROMPT),
+      help = STRING_TOKEN(CHECKBOX_HELP),
+      default = TRUE, defaultstore = StandardDefault,
+      default = FALSE, defaultstore = ManufactureDefault,
+    endcheckbox;
+
+    numeric
+      name = NumericQuestion,
+      varid = FormData.NumericValue,
+      prompt = STRING_TOKEN(NUMERIC_PROMPT),
+      help = STRING_TOKEN(NUMERIC_HELP),
+      flags = NUMERIC_SIZE_2 | DISPLAY_UINT_HEX,
+      //minimum = 0x1234,
+      //maximum = 0xaa55,
+      minimum = 0,
+      maximum = 10,
+      step = 1,
+      default = 7, defaultstore = StandardDefault,
+      default = 8, defaultstore = ManufactureDefault,
+    endnumeric;
+
+    string
+      name = StringQuestion,
+      varid = FormData.StringValue,
+      prompt = STRING_TOKEN(STRING_PROMPT),
+      help = STRING_TOKEN(STRING_HELP),
+      minsize = 5,
+      maxsize = 10,
+      default = STRING_TOKEN(STRING_DEFAULT), defaultstore = StandardDefault,
+      default = STRING_TOKEN(STRING_PROMPT), defaultstore = ManufactureDefault,
+    endstring;
+
+    date
+      varid = FormData.DateValue,
+      prompt = STRING_TOKEN(DATE_PROMPT),
+      help = STRING_TOKEN(DATE_HELP),
+      default = 2021/05/22,
+    enddate;
+
+    time
+      varid = FormData.TimeValue,
+      prompt = STRING_TOKEN(TIME_PROMPT),
+      help = STRING_TOKEN(TIME_HELP),
+      default = 23:55:33,
+    endtime;
+
+    oneof
+      name = OneOfQuestion,
+      varid = FormData.OneOfValue,
+      prompt = STRING_TOKEN(ONEOF_PROMPT),
+      help = STRING_TOKEN(ONEOF_HELP),
+      option text = STRING_TOKEN(ONEOF_OPTION1), value = 0x00, flags = 0;
+      option text = STRING_TOKEN(ONEOF_OPTION2), value = 0x33, flags = MANUFACTURING;
+      option text = STRING_TOKEN(ONEOF_OPTION3), value = 0x55, flags = DEFAULT;
+    endoneof;
+
+    orderedlist
+      varid = FormData.OrderedListValue,
+      prompt = STRING_TOKEN(ORDERED_LIST_PROMPT),
+      help = STRING_TOKEN(ORDERED_LIST_HELP),
+      option text = STRING_TOKEN(ORDERED_LIST_OPTION1), value = 0x0A, flags = 0;
+      option text = STRING_TOKEN(ORDERED_LIST_OPTION2), value = 0x0B, flags = 0;
+      option text = STRING_TOKEN(ORDERED_LIST_OPTION3), value = 0x0C, flags = 0;
+      default = {0x0c, 0x0b, 0x0a},
+    endlist;
+
+    resetbutton
+      defaultstore = StandardDefault,
+      prompt   = STRING_TOKEN(BTN_STANDARD_DEFAULT_PROMPT),
+      help     = STRING_TOKEN(BTN_STANDARD_DEFAULT_HELP),
+    endresetbutton;
+
+    resetbutton
+      defaultstore = ManufactureDefault,
+      prompt   = STRING_TOKEN(BTN_MFG_DEFAULT_PROMPT),
+      help     = STRING_TOKEN(BTN_MFG_DEFAULT_HELP),
+    endresetbutton;
+  endform;
+endformset;
+```
+
+DevicePath is also encoded like `VenHw(FORMSET_GUID)` (`UefiLessonsPkg/HIIFormDataElements/HIIFormDataElements.c`):
+```cpp
+HII_VENDOR_DEVICE_PATH  mHiiVendorDevicePath = {
+  {
+    {
+      HARDWARE_DEVICE_PATH,
+      HW_VENDOR_DP,
+      {
+        (UINT8) (sizeof (VENDOR_DEVICE_PATH)),
+        (UINT8) ((sizeof (VENDOR_DEVICE_PATH)) >> 8)
+      }
+    },
+    FORMSET_GUID
+  },
+  {
+    END_DEVICE_PATH_TYPE,
+    END_ENTIRE_DEVICE_PATH_SUBTYPE,
+    {
+      (UINT8) (END_DEVICE_PATH_LENGTH),
+      (UINT8) ((END_DEVICE_PATH_LENGTH) >> 8)
+    }
+  }
+};
+```
+
+Let's try to load the driver to the environment:
+```
+FS0:\> load HIIFormDataElements.efi
+```
+
+And request its HII configuration data:
+```
+FS0:\> HIIConfig.efi extract 531bc507-9191-4fa2-9446-b844e35dd12a FormData VenHw(531bc507-9191-4fa2-9446-b844e35dd12a)
+
+Request: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400
+Response: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=0000&WIDTH=0001&VALUE=00&OFFSET=0001&WIDTH=0002&VALUE=0000&OFFSET=0003&WIDTH=0014&VALUE=0000000000000000000000000000000000000000&OFFSET=0019&WIDTH=0004&VALUE=00000000&OFFSET=001<...>
+
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+OFFSET=0001  WIDTH=0002  VALUE=0000
+00 00                                            | ..
+OFFSET=0003  WIDTH=0014  VALUE=0000000000000000000000000000000000000000
+00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  | ................
+00 00 00 00                                      | ....
+OFFSET=0019  WIDTH=0004  VALUE=00000000
+00 00 00 00                                      | ....
+OFFSET=001d  WIDTH=0003  VALUE=000000
+00 00 00                                         | ...
+OFFSET=0020  WIDTH=0001  VALUE=00
+00                                               | .
+OFFSET=0021  WIDTH=0003  VALUE=000000
+00 00 00                                         | ...
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0000
+OFFSET=0000  WIDTH=0001  VALUE=01
+01                                               | .
+OFFSET=0001  WIDTH=0002  VALUE=0007
+07 00                                            | ..
+OFFSET=0003  WIDTH=0014  VALUE=00660065006400200067006e0069007200740053
+53 00 74 00 72 00 69 00 6E 00 67 00 20 00 64 00  | S.t.r.i.n.g. .d.
+65 00 66 00                                      | e.f.
+OFFSET=0019  WIDTH=0004  VALUE=160507e5
+E5 07 05 16                                      | ....
+OFFSET=001d  WIDTH=0003  VALUE=213717
+17 37 21                                         | .7!
+OFFSET=0020  WIDTH=0001  VALUE=55
+55                                               | U
+OFFSET=0021  WIDTH=0003  VALUE=0a0b0c
+0C 0B 0A                                         | ...
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0001
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+OFFSET=0001  WIDTH=0002  VALUE=0008
+08 00                                            | ..
+OFFSET=0003  WIDTH=0014  VALUE=006f0072007000200067006e0069007200740053
+53 00 74 00 72 00 69 00 6E 00 67 00 20 00 70 00  | S.t.r.i.n.g. .p.
+72 00 6F 00                                      | r.o.
+OFFSET=0019  WIDTH=0004  VALUE=160507e5
+E5 07 05 16                                      | ....
+OFFSET=001d  WIDTH=0003  VALUE=213717
+17 37 21                                         | .7!
+OFFSET=0020  WIDTH=0001  VALUE=33
+33                                               | 3
+OFFSET=0021  WIDTH=0003  VALUE=0a0b0c
+0C 0B 0A                                         | ...
+```
+
+Here you can see the current values (by default they are all zeros), and the Standard and Manufacturing defaults. As we've actually filled defaults in the VFR code, you can see different data for the Standard and Manufacturing cases.
+
+You can request individual form elements if you provide offset and width in the request. For example here is how you can get settings for the `string` element:
+```
+FS0:\> HIIConfig.efi extract 531bc507-9191-4fa2-9446-b844e35dd12a FormData VenHw(531bc507-9191-4fa2-9446-b844e35dd12a) 3 14
+Request: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=3&WIDTH=14
+Response: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=3&WIDTH=14&VALUE=0000000000000000000000000000000000000000&GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd1<...>
+
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+OFFSET=3  WIDTH=14  VALUE=0000000000000000000000000000000000000000
+00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  | ................
+00 00 00 00                                      | ....
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0000
+OFFSET=0003  WIDTH=0014  VALUE=00660065006400200067006e0069007200740053
+53 00 74 00 72 00 69 00 6E 00 67 00 20 00 64 00  | S.t.r.i.n.g. .d.
+65 00 66 00                                      | e.f.
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0001
+OFFSET=0003  WIDTH=0014  VALUE=006f0072007000200067006e0069007200740053
+53 00 74 00 72 00 69 00 6E 00 67 00 20 00 70 00  | S.t.r.i.n.g. .p.
+72 00 6F 00                                      | r.o.
+```
+
+It is not required that `OFFSET...OFFSET+WIDTH` should be on the element boundaries. You can provide any OFFSET/WIDTH combination that defines a range within the storage limits. For example `0 2` would include the `checkbox` and a part of the `numeric` element:
+```
+FS0:\> HIIConfig.efi extract 531bc507-9191-4fa2-9446-b844e35dd12a FormData VenHw(531bc507-9191-4fa2-9446-b844e35dd12a) 0 2
+
+Request: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=0&WIDTH=2
+Response: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=0&WIDTH=2&VALUE=0000&GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&ALTCFG=0000&OFFSET=0000&WI<...>
+
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+OFFSET=0  WIDTH=2  VALUE=0000
+00 00                                            | ..
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0000
+OFFSET=0000  WIDTH=0001  VALUE=01
+01                                               | .
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0001
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+```
+
+In such cases `ALTCFG`'s are provided only for the elements that are covered fully by the OFFSET/WIDTH combination. This is why there is `ALTCFG` only for the `checkbox` element, but not for the `numeric` element. If you'll provide `0 3` as OFFSET/WIDTH, both elements would be covered by the range and alternative configurations would be displayed for both of them:
+```
+FS0:\> HIIConfig.efi extract 531bc507-9191-4fa2-9446-b844e35dd12a FormData VenHw(531bc507-9191-4fa2-9446-b844e35dd12a) 0 3
+
+Request: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=0&WIDTH=3
+Response: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=0&WIDTH=3&VALUE=000000&GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&ALTCFG=0000&OFFSET=0000&<...>
+
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+OFFSET=0  WIDTH=3  VALUE=000000
+00 00 00                                         | ...
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0000
+OFFSET=0000  WIDTH=0001  VALUE=01
+01                                               | .
+OFFSET=0001  WIDTH=0002  VALUE=0007
+07 00                                            | ..
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+FS0:\> 46006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+ALTCFG=0001
+OFFSET=0000  WIDTH=0001  VALUE=00
+00                                               | .
+OFFSET=0001  WIDTH=0002  VALUE=0008
+08 00                                            | ..
+```
+
+And if offset/width doesn't cover any element range, there wouldn't be any `ALTCFG`'s in the output at all:
+```
+FS0:\> HIIConfig.efi extract 531bc507-9191-4fa2-9446-b844e35dd12a FormData VenHw(531bc507-9191-4fa2-9446-b844e35dd12a) 12 3
+
+Request: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=12&WIDTH=3
+Response: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=12&WIDTH=3&VALUE=000000
+
+
+GUID=07c51b539191a24f9446b844e35dd12a (531BC507-9191-4FA2-9446-B844E35DD12A)
+NAME=0046006f0072006d0044006100740061 (FormData)
+PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400 (VenHw(531BC507-9191-4FA2-9446-B844E35DD12A))
+OFFSET=12  WIDTH=3  VALUE=000000
+00 00 00                                         | ...
+```
+
+Finally if you'll provide OFFSET/WIDTH that cover range outside of the storage limit, you would get an error:
+```
+FS0:\> HIIConfig.efi extract 531bc507-9191-4fa2-9446-b844e35dd12a FormData VenHw(531bc507-9191-4fa2-9446-b844e35dd12a) 21 9
+
+Request: GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=21&WIDTH=9
+Part of string was unparsed GUID=07c51b539191a24f9446b844e35dd12a&NAME=0046006f0072006d0044006100740061&PATH=0104140007c51b539191a24f9446b844e35dd12a7fff0400&OFFSET=21&WIDTH=9
+Error! ExtractConfig returned Device Error
+```
+
+You can try to modify form element values via the form browser and look how `extract` response correctly displays the new data.
+
diff --git a/README.md b/README.md
index 924c08f..e565c7e 100644
--- a/README.md
+++ b/README.md
@@ -81,6 +81,7 @@ _____
 - [Lesson XX](Lessons_uncategorized/Lesson_Configuration_Language_1): UEFI Configuration language. Dump current HII Database settings with the `EFI_HII_CONFIG_ROUTING_PROTOCOL.ExportConfig()` function
 - [Lesson XX](Lessons_uncategorized/Lesson_Configuration_Language_2): UEFI Configuration language. Create a function to prettify configuration string data 
 - [Lesson XX](Lessons_uncategorized/Lesson_Configuration_Language_3): UEFI Configuration language. Extract individual form element configurations with the `EFI_HII_CONFIG_ROUTING_PROTOCOL.ExtractConfig()` function
+- [Lesson XX](Lessons_uncategorized/Lesson_Configuration_Language_4): UEFI Configuration language. Explore `ExtractConfig` request syntax on custom forms
 _____
 - [Lesson XX](Lessons_uncategorized/Lesson_ARCH): Architecture specifier in section names
 - [Lesson XX](Lessons_uncategorized/Lesson_SKU): SKU specifier in section names