src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriver.cs

@@ -1025,10 +1025,31 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                 if (tag.DataType == AbCipDataType.Structure && tag.Members is { Count: > 0 })
                 {
                     var udtFolder = deviceFolder.Folder(tag.Name, tag.Name);
+                    // PR abcip-2.6 — AOI-aware fan-out. When any member carries a non-Local
+                    // AoiQualifier the tag is treated as an AOI instance: Input / Output / InOut
+                    // members get grouped under sub-folders (Inputs/, Outputs/, InOut/) so the
+                    // browse tree visually matches Studio 5000's AOI parameter tabs. Plain UDT
+                    // tags (every member Local) retain the pre-2.6 flat layout under the parent
+                    // folder so existing browse paths stay stable.
+                    var hasDirectional = tag.Members.Any(m => m.AoiQualifier != AoiQualifier.Local);
+                    IAddressSpaceBuilder? inputsFolder = null;
+                    IAddressSpaceBuilder? outputsFolder = null;
+                    IAddressSpaceBuilder? inOutFolder = null;
                     foreach (var member in tag.Members)
                     {
+                        var parentFolder = udtFolder;
+                        if (hasDirectional)
+                        {
+                            parentFolder = member.AoiQualifier switch
+                            {
+                                AoiQualifier.Input => inputsFolder ??= udtFolder.Folder("Inputs", "Inputs"),
+                                AoiQualifier.Output => outputsFolder ??= udtFolder.Folder("Outputs", "Outputs"),
+                                AoiQualifier.InOut => inOutFolder ??= udtFolder.Folder("InOut", "InOut"),
+                                _ => udtFolder, // Local stays at the AOI root
+                            };
+                        }
                         var memberFullName = $"{tag.Name}.{member.Name}";
-                        udtFolder.Variable(member.Name, member.Name, new DriverAttributeInfo(
+                        parentFolder.Variable(member.Name, member.Name, new DriverAttributeInfo(
                             FullName: memberFullName,
                             DriverDataType: member.DataType.ToDriverDataType(),
                             IsArray: false,

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriverOptions.cs

@@ -153,9 +153,14 @@ public sealed record AbCipTagDefinition(
 ///     (class 0x6C) that would auto-discover member layouts lands as a follow-up PR.
 /// </summary>
 /// <remarks>
-///     <see cref="Description"/> carries the per-member comment from L5K/L5X UDT definitions so
+///     <para><see cref="Description"/> carries the per-member comment from L5K/L5X UDT definitions so
 ///     the OPC UA Variable nodes produced for individual members surface their descriptions too,
-///     not just the top-level tag.
+///     not just the top-level tag.</para>
+///     <para>PR abcip-2.6 — <see cref="AoiQualifier"/> tags AOI parameters as Input / Output /
+///     InOut / Local. Plain UDT members default to <see cref="AoiQualifier.Local"/>. Discovery
+///     groups Input / Output / InOut members under sub-folders so an AOI-typed tag fans out as
+///     <c>Tag/Inputs/...</c>, <c>Tag/Outputs/...</c>, <c>Tag/InOut/...</c> while Local stays at the
+///     UDT root — matching how AOIs visually present in Studio 5000.</para>
 /// </remarks>
 public sealed record AbCipStructureMember(
     string Name,
@@ -163,7 +168,30 @@ public sealed record AbCipStructureMember(
     bool Writable = true,
     bool WriteIdempotent = false,
     int? StringLength = null,
-    string? Description = null);
+    string? Description = null,
+    AoiQualifier AoiQualifier = AoiQualifier.Local);
+
+/// <summary>
+///     PR abcip-2.6 — directional qualifier for AOI parameters. Surfaces the Studio 5000
+///     <c>Usage</c> attribute (<c>Input</c> / <c>Output</c> / <c>InOut</c>) so discovery can group
+///     AOI members into sub-folders and downstream consumers can reason about parameter direction.
+///     Plain UDT members (non-AOI types) default to <see cref="Local"/>, which keeps them at the
+///     UDT root + indicates they are internal storage rather than a directional parameter.
+/// </summary>
+public enum AoiQualifier
+{
+    /// <summary>UDT member or AOI local tag — non-directional, browsed at the parent's root.</summary>
+    Local,
+
+    /// <summary>AOI input parameter — written by the caller, read by the AOI body.</summary>
+    Input,
+
+    /// <summary>AOI output parameter — written by the AOI body, read by the caller.</summary>
+    Output,
+
+    /// <summary>AOI bidirectional parameter — passed by reference, both sides may read/write.</summary>
+    InOut,
+}
 
 /// <summary>
 ///     One L5K-import entry. Either <see cref="FilePath"/> or <see cref="InlineText"/> must be

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/Import/L5kIngest.cs

@@ -59,7 +59,8 @@ public sealed class L5kIngest
                     Name: m.Name,
                     DataType: memberType,
                     Writable: writable,
-                    Description: m.Description));
+                    Description: m.Description,
+                    AoiQualifier: MapAoiUsage(m.Usage)));
             }
             udtIndex[dt.Name] = members;
         }
@@ -119,6 +120,19 @@ public sealed class L5kIngest
     private static bool IsAccessNone(string? externalAccess) =>
         externalAccess is not null && externalAccess.Trim().Equals("None", StringComparison.OrdinalIgnoreCase);
 
+    /// <summary>
+    ///     PR abcip-2.6 — map the AOI <c>Usage</c> attribute string to <see cref="AoiQualifier"/>.
+    ///     Plain UDT members (Usage = null) + unrecognised values map to <see cref="AoiQualifier.Local"/>.
+    /// </summary>
+    private static AoiQualifier MapAoiUsage(string? usage) =>
+        usage?.Trim().ToUpperInvariant() switch
+        {
+            "INPUT" => AoiQualifier.Input,
+            "OUTPUT" => AoiQualifier.Output,
+            "INOUT" => AoiQualifier.InOut,
+            _ => AoiQualifier.Local,
+        };
+
     /// <summary>Map a Logix atomic type name. Returns <c>null</c> for UDT/structure references.</summary>
     private static AbCipDataType? TryMapAtomic(string logixType) =>
         logixType?.Trim().ToUpperInvariant() switch

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/Import/L5kParser.cs

@@ -72,6 +72,16 @@ public static class L5kParser
                 continue;
             }
 
+            // PR abcip-2.6 — ADD_ON_INSTRUCTION_DEFINITION block. AOI parameters carry a Usage
+            // attribute (Input / Output / InOut); each PARAMETER becomes a member of the AOI's
+            // L5kDataType entry so AOI-typed tags pick up a layout the same way UDT-typed tags do.
+            if (StartsWithKeyword(line, "ADD_ON_INSTRUCTION_DEFINITION"))
+            {
+                var consumed = ParseAoiDefinitionBlock(lines, i, datatypes);
+                i += consumed;
+                continue;
+            }
+
             i++;
         }
 
@@ -312,7 +322,74 @@ public static class L5kParser
         if (typePart.Length == 0) return null;
         var externalAccess = attributes.TryGetValue("ExternalAccess", out var ea) ? ea.Trim() : null;
         var description = attributes.TryGetValue("Description", out var d) ? Unquote(d) : null;
-        return new L5kMember(name, typePart, arrayDim, externalAccess, description);
+        // PR abcip-2.6 — Usage attribute on AOI parameters (Input / Output / InOut). Plain UDT
+        // members don't carry it; null on a regular DATATYPE MEMBER is the default + maps to Local
+        // in the ingest layer.
+        var usage = attributes.TryGetValue("Usage", out var u) ? u.Trim() : null;
+        return new L5kMember(name, typePart, arrayDim, externalAccess, description, usage);
+    }
+
+    // ---- AOI block ---------------------------------------------------------
+
+    /// <summary>
+    ///     PR abcip-2.6 — parse <c>ADD_ON_INSTRUCTION_DEFINITION ... END_ADD_ON_INSTRUCTION_DEFINITION</c>
+    ///     blocks. Body is structured around PARAMETER entries (each carrying a <c>Usage</c>
+    ///     attribute) and optional LOCAL_TAGS / ROUTINE blocks. We extract the parameters as
+    ///     <see cref="L5kMember"/> rows + leave routines alone — only the surface API matters for
+    ///     tag-discovery fan-out. The L5K format encloses parameters either inside a
+    ///     <c>PARAMETERS ... END_PARAMETERS</c> block or as bare <c>PARAMETER ... ;</c> lines at
+    ///     the AOI top level depending on Studio 5000 export options; this parser accepts both.
+    /// </summary>
+    private static int ParseAoiDefinitionBlock(string[] lines, int start, List<L5kDataType> into)
+    {
+        var first = lines[start].Trim();
+        var head = first.Substring("ADD_ON_INSTRUCTION_DEFINITION".Length).Trim();
+        var name = ExtractFirstQuotedOrToken(head);
+        var members = new List<L5kMember>();
+        var i = start + 1;
+        var inLocalsBlock = false;
+        var inRoutineBlock = false;
+        while (i < lines.Length)
+        {
+            var line = lines[i].Trim();
+            if (StartsWithKeyword(line, "END_ADD_ON_INSTRUCTION_DEFINITION"))
+            {
+                if (!string.IsNullOrEmpty(name)) into.Add(new L5kDataType(name, members));
+                return i - start + 1;
+            }
+            if (line.Length == 0) { i++; continue; }
+
+            // Skip routine bodies — they hold ladder / ST / FBD code we don't care about for
+            // tag-discovery, and their own END_ROUTINE / END_LOCAL_TAGS tokens close them out.
+            if (StartsWithKeyword(line, "ROUTINE")) { inRoutineBlock = true; i++; continue; }
+            if (StartsWithKeyword(line, "END_ROUTINE")) { inRoutineBlock = false; i++; continue; }
+            if (StartsWithKeyword(line, "LOCAL_TAGS")) { inLocalsBlock = true; i++; continue; }
+            if (StartsWithKeyword(line, "END_LOCAL_TAGS")) { inLocalsBlock = false; i++; continue; }
+            if (inRoutineBlock || inLocalsBlock) { i++; continue; }
+
+            // PARAMETERS / END_PARAMETERS wrappers are skipped — bare PARAMETER lines drive parsing.
+            if (StartsWithKeyword(line, "PARAMETERS")) { i++; continue; }
+            if (StartsWithKeyword(line, "END_PARAMETERS")) { i++; continue; }
+
+            if (StartsWithKeyword(line, "PARAMETER"))
+            {
+                var sb = new System.Text.StringBuilder(line);
+                while (!sb.ToString().TrimEnd().EndsWith(';') && i + 1 < lines.Length)
+                {
+                    var peek = lines[i + 1].Trim();
+                    if (StartsWithKeyword(peek, "END_ADD_ON_INSTRUCTION_DEFINITION")) break;
+                    i++;
+                    sb.Append(' ').Append(peek);
+                }
+                var entry = sb.ToString().TrimEnd(';').Trim();
+                entry = entry.Substring("PARAMETER".Length).Trim();
+                var member = ParseMemberEntry(entry);
+                if (member is not null) members.Add(member);
+            }
+            i++;
+        }
+        if (!string.IsNullOrEmpty(name)) into.Add(new L5kDataType(name, members));
+        return i - start;
     }
 
     // ---- helpers -----------------------------------------------------------
@@ -377,10 +454,16 @@ public sealed record L5kTag(
 /// <summary>One UDT definition extracted from a <c>DATATYPE ... END_DATATYPE</c> block.</summary>
 public sealed record L5kDataType(string Name, IReadOnlyList<L5kMember> Members);
 
-/// <summary>One member line inside a UDT definition.</summary>
+/// <summary>One member line inside a UDT definition or AOI parameter list.</summary>
+/// <remarks>
+///     PR abcip-2.6 — <see cref="Usage"/> carries the AOI <c>Usage</c> attribute (<c>Input</c> /
+///     <c>Output</c> / <c>InOut</c>) raw text. Plain UDT members + L5K AOI <c>LOCAL_TAGS</c> leave
+///     it null; the ingest layer maps null → <see cref="AoiQualifier.Local"/>.
+/// </remarks>
 public sealed record L5kMember(
     string Name,
     string DataType,
     int? ArrayDim,
     string? ExternalAccess,
-    string? Description = null);
+    string? Description = null,
+    string? Usage = null);

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/Import/L5xParser.cs

@@ -218,12 +218,19 @@ public static class L5xParser
                 if (!string.IsNullOrEmpty(raw)) paramDescription = raw.Trim();
             }
 
+            // PR abcip-2.6 — capture the AOI Usage attribute (Input / Output / InOut). RSLogix
+            // also serialises Local AOI tags inside <LocalTags>, but those don't go through this
+            // path — only <Parameters>/<Parameter> entries do — so any Usage value on a parameter
+            // is one of the directional buckets.
+            var usage = paramNode.GetAttribute("Usage", string.Empty);
+
             members.Add(new L5kMember(
                 Name: paramName,
                 DataType: dataType,
                 ArrayDim: arrayDim,
                 ExternalAccess: string.IsNullOrEmpty(externalAccess) ? null : externalAccess,
-                Description: paramDescription));
+                Description: paramDescription,
+                Usage: string.IsNullOrEmpty(usage) ? null : usage));
         }
         return new L5kDataType(name, members);
     }

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipUdtMemberTests.cs

@@ -167,6 +167,83 @@ public sealed class AbCipUdtMemberTests
         builder.Variables.ShouldContain(v => v.BrowseName == "EmptyUdt");
     }
 
+    [Fact]
+    public async Task AOI_typed_tag_groups_members_under_directional_subfolders()
+    {
+        // PR abcip-2.6 — when any member carries a non-Local AoiQualifier, the tag is treated
+        // as an AOI instance: Input / Output / InOut members get grouped under sub-folders so
+        // the browse tree mirrors Studio 5000's AOI parameter tabs. Plain UDT tags (every member
+        // Local) keep the pre-2.6 flat layout.
+        var builder = new RecordingBuilder();
+        var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags =
+            [
+                new AbCipTagDefinition(
+                    Name: "Valve_001",
+                    DeviceHostAddress: "ab://10.0.0.5/1,0",
+                    TagPath: "Valve_001",
+                    DataType: AbCipDataType.Structure,
+                    Members:
+                    [
+                        new AbCipStructureMember("Cmd", AbCipDataType.Bool, AoiQualifier: AoiQualifier.Input),
+                        new AbCipStructureMember("Status", AbCipDataType.DInt, Writable: false, AoiQualifier: AoiQualifier.Output),
+                        new AbCipStructureMember("Buffer", AbCipDataType.DInt, AoiQualifier: AoiQualifier.InOut),
+                        new AbCipStructureMember("LocalVar", AbCipDataType.DInt, AoiQualifier: AoiQualifier.Local),
+                    ]),
+            ],
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        // Sub-folders for each directional bucket land in the recorder; the AOI parent folder
+        // and the Local member's lack of a sub-folder confirm only directional members get
+        // bucketed. Folder names are intentionally simple (Inputs / Outputs / InOut) — clients
+        // that browse "Valve_001/Inputs/Cmd" see exactly that path.
+        builder.Folders.Select(f => f.BrowseName).ShouldContain("Valve_001");
+        builder.Folders.Select(f => f.BrowseName).ShouldContain("Inputs");
+        builder.Folders.Select(f => f.BrowseName).ShouldContain("Outputs");
+        builder.Folders.Select(f => f.BrowseName).ShouldContain("InOut");
+
+        // Variables emitted under the right full names — full reference still {Tag}.{Member}
+        // so the read/write paths stay unchanged from the flat-UDT case.
+        var variables = builder.Variables.Select(v => (v.BrowseName, v.Info.FullName)).ToList();
+        variables.ShouldContain(("Cmd", "Valve_001.Cmd"));
+        variables.ShouldContain(("Status", "Valve_001.Status"));
+        variables.ShouldContain(("Buffer", "Valve_001.Buffer"));
+        variables.ShouldContain(("LocalVar", "Valve_001.LocalVar"));
+    }
+
+    [Fact]
+    public async Task Plain_UDT_keeps_flat_layout_when_every_member_is_Local()
+    {
+        // Plain UDTs (no Usage attributes anywhere) stay on the pre-2.6 flat layout — no
+        // Inputs/Outputs/InOut sub-folders should appear since there are no directional members.
+        var builder = new RecordingBuilder();
+        var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags =
+            [
+                new AbCipTagDefinition("Tank1", "ab://10.0.0.5/1,0", "Tank1", AbCipDataType.Structure,
+                    Members:
+                    [
+                        new AbCipStructureMember("Level", AbCipDataType.Real),
+                        new AbCipStructureMember("Pressure", AbCipDataType.Real),
+                    ]),
+            ],
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        builder.Folders.Select(f => f.BrowseName).ShouldNotContain("Inputs");
+        builder.Folders.Select(f => f.BrowseName).ShouldNotContain("Outputs");
+        builder.Folders.Select(f => f.BrowseName).ShouldNotContain("InOut");
+    }
+
     [Fact]
     public async Task UDT_members_mixed_with_flat_tags_coexist()
     {

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/L5kIngestTests.cs

@@ -153,6 +153,81 @@ public sealed class L5kIngestTests
         Should.Throw<InvalidOperationException>(() => new L5kIngest().Ingest(doc));
     }
 
+    [Fact]
+    public void AOI_member_Usage_maps_to_AoiQualifier_through_ingest()
+    {
+        // PR abcip-2.6 — L5K AOI parameters carry a Usage := Input / Output / InOut attribute.
+        // Ingest must map those values onto AbCipStructureMember.AoiQualifier so the discovery
+        // layer can group AOI members under sub-folders. Plain DATATYPE members get Local.
+        const string body = """
+            ADD_ON_INSTRUCTION_DEFINITION ValveAoi
+                PARAMETERS
+                    PARAMETER Cmd : BOOL (Usage := Input) := 0;
+                    PARAMETER Status : DINT (Usage := Output) := 0;
+                    PARAMETER Buffer : DINT (Usage := InOut) := 0;
+                    PARAMETER Local1 : DINT := 0;
+                END_PARAMETERS
+            END_ADD_ON_INSTRUCTION_DEFINITION
+            DATATYPE PlainUdt
+                MEMBER Speed : DINT := 0;
+            END_DATATYPE
+            TAG
+                Valve_001 : ValveAoi;
+                Tank1 : PlainUdt;
+            END_TAG
+            """;
+        var doc = L5kParser.Parse(new StringL5kSource(body));
+
+        var result = new L5kIngest { DefaultDeviceHostAddress = DeviceHost }.Ingest(doc);
+
+        var aoiTag = result.Tags.Single(t => t.Name == "Valve_001");
+        aoiTag.Members.ShouldNotBeNull();
+        aoiTag.Members!.Single(m => m.Name == "Cmd").AoiQualifier.ShouldBe(AoiQualifier.Input);
+        aoiTag.Members.Single(m => m.Name == "Status").AoiQualifier.ShouldBe(AoiQualifier.Output);
+        aoiTag.Members.Single(m => m.Name == "Buffer").AoiQualifier.ShouldBe(AoiQualifier.InOut);
+        aoiTag.Members.Single(m => m.Name == "Local1").AoiQualifier.ShouldBe(AoiQualifier.Local);
+
+        // Plain UDT members default to Local — no Usage attribute to map.
+        var plainTag = result.Tags.Single(t => t.Name == "Tank1");
+        plainTag.Members.ShouldNotBeNull();
+        plainTag.Members!.Single().AoiQualifier.ShouldBe(AoiQualifier.Local);
+    }
+
+    [Fact]
+    public void L5x_AOI_member_Usage_maps_to_AoiQualifier_through_ingest()
+    {
+        // Same mapping as the L5K case above, exercised through the L5X parser to confirm both
+        // formats land at the same downstream representation.
+        const string body = """
+            <?xml version="1.0" encoding="UTF-8"?>
+            <RSLogix5000Content>
+              <Controller Name="C">
+                <AddOnInstructionDefinitions>
+                  <AddOnInstructionDefinition Name="MyAoi">
+                    <Parameters>
+                      <Parameter Name="Cmd" DataType="BOOL" Usage="Input" />
+                      <Parameter Name="Status" DataType="DINT" Usage="Output" />
+                      <Parameter Name="Buffer" DataType="DINT" Usage="InOut" />
+                    </Parameters>
+                  </AddOnInstructionDefinition>
+                </AddOnInstructionDefinitions>
+                <Tags>
+                  <Tag Name="Valve_001" TagType="Base" DataType="MyAoi" />
+                </Tags>
+              </Controller>
+            </RSLogix5000Content>
+            """;
+        var doc = L5xParser.Parse(new StringL5kSource(body));
+
+        var result = new L5kIngest { DefaultDeviceHostAddress = DeviceHost }.Ingest(doc);
+
+        var aoiTag = result.Tags.Single();
+        aoiTag.Members.ShouldNotBeNull();
+        aoiTag.Members!.Single(m => m.Name == "Cmd").AoiQualifier.ShouldBe(AoiQualifier.Input);
+        aoiTag.Members.Single(m => m.Name == "Status").AoiQualifier.ShouldBe(AoiQualifier.Output);
+        aoiTag.Members.Single(m => m.Name == "Buffer").AoiQualifier.ShouldBe(AoiQualifier.InOut);
+    }
+
     [Fact]
     public void NamePrefix_is_applied_to_imported_tags()
     {

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/L5kParserTests.cs

@@ -150,6 +150,36 @@ public sealed class L5kParserTests
         doc.Tags[0].Name.ShouldBe("Real_Tag");
     }
 
+    [Fact]
+    public void AOI_definition_block_collects_parameters_with_Usage()
+    {
+        // PR abcip-2.6 — ADD_ON_INSTRUCTION_DEFINITION blocks with PARAMETER entries carrying
+        // Usage := Input / Output / InOut. The parser surfaces them as L5kDataType members so
+        // AOI-typed tags pick up a layout the same way UDT-typed tags do.
+        const string body = """
+            ADD_ON_INSTRUCTION_DEFINITION MyValveAoi (Revision := "1.0")
+                PARAMETERS
+                    PARAMETER Cmd : BOOL (Usage := Input) := 0;
+                    PARAMETER Status : DINT (Usage := Output, ExternalAccess := Read Only) := 0;
+                    PARAMETER Buffer : DINT (Usage := InOut) := 0;
+                    PARAMETER Internal : DINT := 0;
+                END_PARAMETERS
+                LOCAL_TAGS
+                    Working : DINT := 0;
+                END_LOCAL_TAGS
+            END_ADD_ON_INSTRUCTION_DEFINITION
+            """;
+
+        var doc = L5kParser.Parse(new StringL5kSource(body));
+
+        var aoi = doc.DataTypes.Single(d => d.Name == "MyValveAoi");
+        aoi.Members.Count.ShouldBe(4);
+        aoi.Members.Single(m => m.Name == "Cmd").Usage.ShouldBe("Input");
+        aoi.Members.Single(m => m.Name == "Status").Usage.ShouldBe("Output");
+        aoi.Members.Single(m => m.Name == "Buffer").Usage.ShouldBe("InOut");
+        aoi.Members.Single(m => m.Name == "Internal").Usage.ShouldBeNull();
+    }
+
     [Fact]
     public void Multi_line_TAG_entry_is_concatenated()
     {

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/L5xParserTests.cs

@@ -191,6 +191,35 @@ public sealed class L5xParserTests
         tag.Members!.Select(m => m.Name).ShouldBe(["Cmd", "Status"]);
     }
 
+    [Fact]
+    public void AOI_parameter_Usage_attribute_is_captured()
+    {
+        // PR abcip-2.6 — Usage attribute on <Parameter> elements (Input / Output / InOut) flows
+        // through to L5kMember.Usage so the ingest layer can map it to AoiQualifier.
+        const string body = """
+            <?xml version="1.0" encoding="UTF-8"?>
+            <RSLogix5000Content>
+              <Controller Name="C">
+                <AddOnInstructionDefinitions>
+                  <AddOnInstructionDefinition Name="MyAoi" Revision="1.0">
+                    <Parameters>
+                      <Parameter Name="Cmd" DataType="BOOL" Usage="Input" />
+                      <Parameter Name="Status" DataType="DINT" Usage="Output" />
+                      <Parameter Name="Buffer" DataType="DINT" Usage="InOut" />
+                    </Parameters>
+                  </AddOnInstructionDefinition>
+                </AddOnInstructionDefinitions>
+              </Controller>
+            </RSLogix5000Content>
+            """;
+
+        var doc = L5xParser.Parse(new StringL5kSource(body));
+        var aoi = doc.DataTypes.Single(d => d.Name == "MyAoi");
+        aoi.Members.Single(m => m.Name == "Cmd").Usage.ShouldBe("Input");
+        aoi.Members.Single(m => m.Name == "Status").Usage.ShouldBe("Output");
+        aoi.Members.Single(m => m.Name == "Buffer").Usage.ShouldBe("InOut");
+    }
+
     [Fact]
     public void Empty_or_minimal_document_returns_empty_bundle_without_throwing()
     {