From 8750c941521801e57241aebf87b1f76e80afef87 Mon Sep 17 00:00:00 2001
From: "christian.vogt@hiquaro.com" <christian.vogt@hiquaro.com>
Date: Sat, 5 Sep 2026 13:18:34 +0200
Subject: [PATCH 1/4] Add CI and trusted publishing workflows, version from git
 tags via MinVer

- ci.yml: build, test and pack on ubuntu and windows for pushes to main and pull requests
- publish.yml: on v* tags pack, verify the package version matches the tag, log in to nuget.org via OIDC (NuGet/login, environment release) and push both packages
- MinVer replaces the hardcoded version; tag prefix v, minimum 5.0, untagged builds are 5.0.x-preview.0.N
- README: CI and NuGet badges

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 .github/workflows/ci.yml      | 51 ++++++++++++++++++++++++++++++
 .github/workflows/publish.yml | 59 +++++++++++++++++++++++++++++++++++
 Directory.Build.props         | 12 ++++++-
 Directory.Packages.props      |  4 +++
 README.md                     |  3 ++
 5 files changed, 128 insertions(+), 1 deletion(-)
 create mode 100644 .github/workflows/ci.yml
 create mode 100644 .github/workflows/publish.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..848c3d2
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,51 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0 # MinVer reads the version from git tags
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v6
+        with:
+          dotnet-version: |
+            8.0.x
+            9.0.x
+            10.0.x
+
+      - name: Restore
+        run: dotnet restore holonsoft.CmdLineParser.slnx
+
+      - name: Build
+        run: dotnet build holonsoft.CmdLineParser.slnx -c Release --no-restore
+
+      - name: Test
+        run: dotnet test holonsoft.CmdLineParser.Tests/holonsoft.CmdLineParser.Tests.csproj -c Release --no-build
+
+      - name: Pack
+        run: dotnet pack holonsoft.CmdLineParser.slnx -c Release --no-build -o artifacts
+
+      - name: Upload packages
+        if: matrix.os == 'ubuntu-latest'
+        uses: actions/upload-artifact@v7
+        with:
+          name: packages
+          path: artifacts/*.nupkg
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
new file mode 100644
index 0000000..f240cd8
--- /dev/null
+++ b/.github/workflows/publish.yml
@@ -0,0 +1,59 @@
+name: Publish to NuGet
+
+# Triggered by version tags such as v5.0.0 or v5.1.0-preview.1.
+# Authenticates against nuget.org with trusted publishing (OIDC), no API key is stored anywhere.
+# The nuget.org policy matches this file name (publish.yml) and the environment name (release).
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: read
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    environment: release
+    permissions:
+      id-token: write # required for the OIDC token that NuGet/login exchanges
+      contents: read
+
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0 # MinVer reads the version from git tags
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v6
+        with:
+          dotnet-version: |
+            8.0.x
+            9.0.x
+            10.0.x
+
+      - name: Build
+        run: dotnet build holonsoft.CmdLineParser.slnx -c Release
+
+      - name: Test
+        run: dotnet test holonsoft.CmdLineParser.Tests/holonsoft.CmdLineParser.Tests.csproj -c Release --no-build
+
+      - name: Pack
+        run: dotnet pack holonsoft.CmdLineParser.slnx -c Release --no-build -o artifacts
+
+      - name: Verify package version matches the tag
+        run: |
+          expected="${GITHUB_REF_NAME#v}"
+          ls -l artifacts
+          test -f "artifacts/holonsoft.CmdLineParser.${expected}.nupkg"
+          test -f "artifacts/holonsoft.CmdLineParser.Abstractions.${expected}.nupkg"
+
+      - name: NuGet login (OIDC)
+        id: login
+        uses: NuGet/login@v1
+        with:
+          user: ${{ secrets.NUGET_USER }} # nuget.org profile name, not the email
+
+      - name: Push to nuget.org
+        run: dotnet nuget push "artifacts/*.nupkg" --api-key ${{ steps.login.outputs.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate
diff --git a/Directory.Build.props b/Directory.Build.props
index 7f72ceb..cabc943 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -10,7 +10,6 @@
   </PropertyGroup>
 
   <PropertyGroup Label="Package metadata">
-    <Version>5.0.0</Version>
     <Company>holonsoft</Company>
     <Authors>Christian Vogt</Authors>
     <Copyright>Christian Vogt, holonsoft</Copyright>
@@ -36,4 +35,15 @@
     <None Include="$(MSBuildThisFileDirectory)README.md" Pack="true" PackagePath="\" Visible="false" />
   </ItemGroup>
 
+  <PropertyGroup Label="Versioning">
+    <!-- MinVer derives the version from git tags (v5.0.0). Untagged commits become 5.0.x-preview.0.N. -->
+    <MinVerTagPrefix>v</MinVerTagPrefix>
+    <MinVerMinimumMajorMinor>5.0</MinVerMinimumMajorMinor>
+    <MinVerDefaultPreReleaseIdentifiers>preview.0</MinVerDefaultPreReleaseIdentifiers>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(IsPackable)' != 'false'">
+    <PackageReference Include="MinVer" PrivateAssets="all" />
+  </ItemGroup>
+
 </Project>
diff --git a/Directory.Packages.props b/Directory.Packages.props
index f6b722a..fce6adb 100644
--- a/Directory.Packages.props
+++ b/Directory.Packages.props
@@ -5,6 +5,10 @@
     <CentralPackageTransitivePinningEnabled>false</CentralPackageTransitivePinningEnabled>
   </PropertyGroup>
 
+  <ItemGroup Label="Build">
+    <PackageVersion Include="MinVer" Version="7.0.0" />
+  </ItemGroup>
+
   <ItemGroup Label="Benchmarks">
     <PackageVersion Include="BenchmarkDotNet" Version="0.15.8" />
   </ItemGroup>
diff --git a/README.md b/README.md
index 55d5be3..ec35006 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,8 @@
 # CmdLineParser
 
+[![CI](https://github.com/holonsoft/CmdLineParser/actions/workflows/ci.yml/badge.svg)](https://github.com/holonsoft/CmdLineParser/actions/workflows/ci.yml)
+[![NuGet](https://img.shields.io/nuget/v/holonsoft.CmdLineParser.svg)](https://www.nuget.org/packages/holonsoft.CmdLineParser/)
+
 Reflection based fast command line parser (`args[]` -> POCO).
 
 Define a class, put attributes on its public fields or properties, call `Parse`. You get a filled object, a list of structured errors and a help text. No builder DSL, no handlers, no ceremony.

From 7fe3b49cb6aae18ca97ce4b2d3d28b2b2eac7368 Mon Sep 17 00:00:00 2001
From: "christian.vogt@hiquaro.com" <christian.vogt@hiquaro.com>
Date: Sun, 6 Sep 2026 09:51:30 +0200
Subject: [PATCH 2/4] Ignore editor-local .vscode folder

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 .gitignore | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/.gitignore b/.gitignore
index b21e17b..55b9ca8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -344,3 +344,6 @@ healthchecksdb
 # Backup folder for Package Reference Convert tool in Visual Studio 2017
 MigrationBackup/
 /Acs.BackendHost/app.config
+
+# Editor-local settings
+.vscode/

From e2c9fa791c875f51699e0ad93ee5d6049547d24b Mon Sep 17 00:00:00 2001
From: "christian.vogt@hiquaro.com" <christian.vogt@hiquaro.com>
Date: Sun, 6 Sep 2026 09:57:49 +0200
Subject: [PATCH 3/4] Fix MustExist test on Unix: absolute paths must not be
 read as slash options

Path.GetTempFileName() returns /tmp/... on Linux, which the default AllowSlashPrefix=true
option turned into an option token. The test now disables the slash prefix explicitly.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 holonsoft.CmdLineParser.Tests/ValidationTests.cs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/holonsoft.CmdLineParser.Tests/ValidationTests.cs b/holonsoft.CmdLineParser.Tests/ValidationTests.cs
index 6c2617d..7007b88 100644
--- a/holonsoft.CmdLineParser.Tests/ValidationTests.cs
+++ b/holonsoft.CmdLineParser.Tests/ValidationTests.cs
@@ -242,7 +242,8 @@ public void MustExistChecksTheFileSystem() {
       var missing = Path.Combine(directory, Guid.NewGuid().ToString("N"));
 
       try {
-         var parser = new CommandLineParser<ExistArgs>();
+         // Absolute paths start with a slash on Unix, which the default options would read as an option prefix.
+         var parser = new CommandLineParser<ExistArgs>(new CommandLineParserOptions { AllowSlashPrefix = false });
 
          Assert.Empty(parser.ParseArguments(["-File", file, "-Directory", directory, "-Any", file]).Errors);
 

From 3a4d43911c0ddc311510b72ae54e2bbf8f43253a Mon Sep 17 00:00:00 2001
From: "christian.vogt@hiquaro.com" <christian.vogt@hiquaro.com>
Date: Sun, 6 Sep 2026 12:01:11 +0200
Subject: [PATCH 4/4] Enable the slash prefix by default on Windows only

Absolute paths start with '/' on Unix-like systems, so a default of AllowSlashPrefix=true
turned every path value into an option token there. The default is now OperatingSystem.IsWindows().
Tests that use the classic /name syntax enable the prefix explicitly, the lexer tests cover the default,
the enabled and the disabled behavior, and the fuzz test exercises both settings on every OS.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 README.md                                     |  5 ++-
 .../ArgumentLexerTests.cs                     | 30 ++++++++++---
 .../CommandLineParserTests.cs                 | 44 +++++++++++--------
 .../EdgeCaseTests.cs                          |  2 +-
 holonsoft.CmdLineParser.Tests/FuzzTests.cs    |  3 ++
 holonsoft.CmdLineParser.Tests/HelpTests.cs    |  2 +-
 .../ValidationTests.cs                        |  3 +-
 .../VerbParserTests.cs                        |  2 +-
 .../CommandLineParserOptions.cs               |  7 +--
 9 files changed, 63 insertions(+), 35 deletions(-)

diff --git a/README.md b/README.md
index ec35006..90f644d 100644
--- a/README.md
+++ b/README.md
@@ -153,7 +153,7 @@ public class Options : IValidatableArguments {
 
 ## Parsing rules
 
-* `-name`, `--name` and `/name` are equivalent. `/` can be disabled in the options for Unix style tools.
+* `-name` and `--name` are equivalent. `/name` is accepted too when `AllowSlashPrefix` is on. That is the default on Windows only, because absolute paths start with `/` on Unix-like systems.
 * A value can follow as separate token or inline: `-name value`, `-name:value`, `-name=value`. Only the first separator counts, so `-url:http://x` works.
 * Values wrapped in double quotes are unquoted.
 * Negative numbers do not need quotes: `-Value -5`, `-Points -1.5 -.5 2`.
@@ -234,7 +234,7 @@ switch (result.Value) {
 ```csharp
 var options = new CommandLineParserOptions {
    IgnoreCase = true,                       // default false
-   AllowSlashPrefix = false,                // default true
+   AllowSlashPrefix = true,                 // default: true on Windows, false elsewhere
    ValueSeparators = [':', '='],            // default
    RecognizeEndOfOptionsMarker = true,      // default
    AutoHelp = true,                         // default
@@ -278,6 +278,7 @@ Breaking changes in 5.0:
 * Empty `args` applies defaults and checks required arguments.
 * Built-in help names `help`, `h` and `?` are recognized unless your class defines them.
 * `--name=value`, unquoted negative numbers and `@file` response files are recognized. A bare `--` ends the options.
+* `/name` is recognized by default on Windows only. Set `AllowSlashPrefix = true` to keep it on Linux and macOS.
 * `Uri`, `Version`, `FileInfo`, `DirectoryInfo` and many more types are supported. Byte overflow is an error instead of silent truncation.
 * The `Argument` class was removed from the Abstractions package. `ArgumentAttribute` string properties are nullable. Missing required arguments are reported once, not once per alias.
 * `GetHelpTexts()` returns empty strings instead of null for missing parts and sorts case-insensitively.
diff --git a/holonsoft.CmdLineParser.Tests/ArgumentLexerTests.cs b/holonsoft.CmdLineParser.Tests/ArgumentLexerTests.cs
index 30126ba..9bbd451 100644
--- a/holonsoft.CmdLineParser.Tests/ArgumentLexerTests.cs
+++ b/holonsoft.CmdLineParser.Tests/ArgumentLexerTests.cs
@@ -13,9 +13,7 @@ private static ArgumentLexer Create(Action<CommandLineParserOptions>? configure
    [Theory]
    [InlineData("-name", "name")]
    [InlineData("--name", "name")]
-   [InlineData("/name", "name")]
    [InlineData("-n", "n")]
-   [InlineData("/?", "?")]
    [InlineData("- name ", "name")]
    public void OptionPrefixes(string raw, string expectedName) {
       var token = Create().Classify(raw, afterEndOfOptions: false);
@@ -28,7 +26,6 @@ public void OptionPrefixes(string raw, string expectedName) {
    [Theory]
    [InlineData("-name:value", "name", "value")]
    [InlineData("--name=value", "name", "value")]
-   [InlineData("/name:\"quoted value\"", "name", "quoted value")]
    [InlineData("-url:http://host:8080/x", "url", "http://host:8080/x")]
    [InlineData("-path=C:\\temp", "path", "C:\\temp")]
    [InlineData("-x:a=b", "x", "a=b")]
@@ -82,11 +79,32 @@ public void EndOfOptionsMarkerCanBeDisabled() {
    }
 
    [Fact]
-   public void SlashPrefixCanBeDisabled() {
-      var token = Create(o => o.AllowSlashPrefix = false).Classify("/etc/passwd", afterEndOfOptions: false);
+   public void SlashPrefixDefaultFollowsTheOperatingSystem() {
+      Assert.Equal(OperatingSystem.IsWindows(), new CommandLineParserOptions().AllowSlashPrefix);
+   }
+
+   [Theory]
+   [InlineData("/name", "name", null)]
+   [InlineData("/?", "?", null)]
+   [InlineData("/name:\"quoted value\"", "name", "quoted value")]
+   [InlineData("/etc/passwd", "etc/passwd", null)]
+   public void SlashPrefixWhenEnabled(string raw, string expectedName, string? expectedValue) {
+      var token = Create(o => o.AllowSlashPrefix = true).Classify(raw, afterEndOfOptions: false);
+
+      Assert.Equal(LexedTokenKind.Option, token.Kind);
+      Assert.Equal(expectedName, token.Name);
+      Assert.Equal(expectedValue, token.Value);
+   }
+
+   [Theory]
+   [InlineData("/name")]
+   [InlineData("/?")]
+   [InlineData("/etc/passwd")]
+   public void SlashPrefixWhenDisabled(string raw) {
+      var token = Create(o => o.AllowSlashPrefix = false).Classify(raw, afterEndOfOptions: false);
 
       Assert.Equal(LexedTokenKind.Value, token.Kind);
-      Assert.Equal("/etc/passwd", token.Value);
+      Assert.Equal(raw, token.Value);
    }
 
    [Fact]
diff --git a/holonsoft.CmdLineParser.Tests/CommandLineParserTests.cs b/holonsoft.CmdLineParser.Tests/CommandLineParserTests.cs
index 158547c..f675a00 100644
--- a/holonsoft.CmdLineParser.Tests/CommandLineParserTests.cs
+++ b/holonsoft.CmdLineParser.Tests/CommandLineParserTests.cs
@@ -11,6 +11,12 @@ namespace holonsoft.CmdLineParser.Tests;
 /// The scenarios of the original test suite, kept as regression guard for the 5.0 rewrite.
 /// </summary>
 public class CommandLineParserTests {
+   /// <summary>
+   /// The original suite mixes '-' and '/' prefixes, so the slash prefix is enabled explicitly. It is off by default on
+   /// Unix-like systems.
+   /// </summary>
+   private static CommandLineParserOptions WithSlashPrefix => new() { AllowSlashPrefix = true };
+
    public static readonly string[] Args1 = ["-s", "--help", "-ka", "\"was das soll\""];
    public static readonly string[] Args2 = ["-c", "huhu", "-d", "-ef", "--h", "/?", "-f", "dummy", "-g", "\"Long text with spaces\"", "/t:test", "dd"];
    public static readonly string[] Args3 = ["-StartConnections", "3", "-MaxConnections:5"];
@@ -56,7 +62,7 @@ public class CommandLineParserTests {
 
    [Fact]
    public void UnknownArgumentsAndHelpDoNotThrow() {
-      var parser = new CommandLineParser<ArgExample1>();
+      var parser = new CommandLineParser<ArgExample1>(WithSlashPrefix);
 
       var result = parser.ParseArguments(Args1);
 
@@ -67,7 +73,7 @@ public void UnknownArgumentsAndHelpDoNotThrow() {
 
    [Fact]
    public void GarbageInputProducesOnlyUnknownArgumentErrors() {
-      var parser = new CommandLineParser<ArgExample1>();
+      var parser = new CommandLineParser<ArgExample1>(WithSlashPrefix);
 
       var result = parser.ParseArguments(Args2);
 
@@ -78,7 +84,7 @@ public void GarbageInputProducesOnlyUnknownArgumentErrors() {
 
    [Fact]
    public void EmptyArgumentsReturnInstanceWithDefaults() {
-      var parser = new CommandLineParser<ArgExample1>();
+      var parser = new CommandLineParser<ArgExample1>(WithSlashPrefix);
 
       var result = parser.Parse([]);
 
@@ -89,7 +95,7 @@ public void EmptyArgumentsReturnInstanceWithDefaults() {
 
    [Fact]
    public void SimpleValuesAndDefaults() {
-      var parser = new CommandLineParser<ArgExample1>();
+      var parser = new CommandLineParser<ArgExample1>(WithSlashPrefix);
       var reported = new List<(ParserErrorKinds Kind, string Hint)>();
 
       var result = parser.Parse(Args3, (kind, hint) => reported.Add((kind, hint)));
@@ -107,7 +113,7 @@ public void SimpleValuesAndDefaults() {
 
    [Fact]
    public void MultiValueCollections() {
-      var parser = new CommandLineParser<CollectionArgs>();
+      var parser = new CommandLineParser<CollectionArgs>(WithSlashPrefix);
 
       var result = parser.Parse(Args4);
 
@@ -119,7 +125,7 @@ public void MultiValueCollections() {
 
    [Fact]
    public void MultipleUniqueCollectionRejectsDuplicates() {
-      var parser = new CommandLineParser<CollectionFail>();
+      var parser = new CommandLineParser<CollectionFail>(WithSlashPrefix);
       var kindOfError = ParserErrorKinds.None;
 
       var result = parser.Parse(Args7, (kind, _) => kindOfError = kind);
@@ -131,7 +137,7 @@ public void MultipleUniqueCollectionRejectsDuplicates() {
 
    [Fact]
    public void UnknownOptionIsReported() {
-      var parser = new CommandLineParser<CollectionFail>();
+      var parser = new CommandLineParser<CollectionFail>(WithSlashPrefix);
       var kindOfError = ParserErrorKinds.None;
 
       parser.Parse(Args8, (kind, _) => kindOfError = kind);
@@ -142,7 +148,7 @@ public void UnknownOptionIsReported() {
 
    [Fact]
    public void FlagWithoutValueIsTrue() {
-      var parser = new CommandLineParser<FlagArg>();
+      var parser = new CommandLineParser<FlagArg>(WithSlashPrefix);
 
       var result = parser.Parse(Args9);
 
@@ -152,7 +158,7 @@ public void FlagWithoutValueIsTrue() {
 
    [Fact]
    public void GuidWithInlineQuotedValue() {
-      var parser = new CommandLineParser<GuidArg>();
+      var parser = new CommandLineParser<GuidArg>(WithSlashPrefix);
 
       var result = parser.Parse(Args5);
 
@@ -162,7 +168,7 @@ public void GuidWithInlineQuotedValue() {
 
    [Fact]
    public void EnumByName() {
-      var parser = new CommandLineParser<EnumArg>();
+      var parser = new CommandLineParser<EnumArg>(WithSlashPrefix);
 
       var result = parser.Parse(Args6);
 
@@ -172,7 +178,7 @@ public void EnumByName() {
 
    [Fact]
    public void MissingRequiredFieldsAreReported() {
-      var parser = new CommandLineParser<ArgExample1>();
+      var parser = new CommandLineParser<ArgExample1>(WithSlashPrefix);
 
       parser.Parse(Args6);
 
@@ -183,7 +189,7 @@ public void MissingRequiredFieldsAreReported() {
 
    [Fact]
    public void AllSupportedTypes() {
-      var parser = new CommandLineParser<AllSupportedTypes>();
+      var parser = new CommandLineParser<AllSupportedTypes>(WithSlashPrefix);
 
       var result = parser.ParseArguments(Args99);
 
@@ -214,7 +220,7 @@ public void AllSupportedTypes() {
 
    [Fact]
    public void HelpTextsListEveryArgument() {
-      var parser = new CommandLineParser<CollectionArgs>();
+      var parser = new CommandLineParser<CollectionArgs>(WithSlashPrefix);
 
       var helpTexts = parser.GetHelpTexts().ToList();
 
@@ -223,14 +229,14 @@ public void HelpTextsListEveryArgument() {
 
    [Fact]
    public void UnsupportedMemberTypeThrowsOnFirstUse() {
-      var parser = new CommandLineParser<UnsupportedTypeArgs>();
+      var parser = new CommandLineParser<UnsupportedTypeArgs>(WithSlashPrefix);
 
       Assert.Throws<NotSupportedException>(() => parser.Parse(["/Anything", "x"]));
    }
 
    [Fact]
    public void ShortNameWithEveryPrefix() {
-      var parser = new CommandLineParser<FlagArg>();
+      var parser = new CommandLineParser<FlagArg>(WithSlashPrefix);
 
       Assert.True(parser.Parse(Args10).FlagWhenFound);
       Assert.True(parser.Parse(Args11).FlagWhenFound);
@@ -239,7 +245,7 @@ public void ShortNameWithEveryPrefix() {
 
    [Fact]
    public void MemberNameLongNameAndShortNameAddressTheSameField() {
-      var parser = new CommandLineParser<DifferentFieldNameArg>();
+      var parser = new CommandLineParser<DifferentFieldNameArg>(WithSlashPrefix);
 
       Assert.Equal("Special_Out1.txt", parser.Parse(Args13).OutFileName);
       Assert.Equal("Special_Out1.txt", parser.Parse(Args14).OutFileName);
@@ -248,7 +254,7 @@ public void MemberNameLongNameAndShortNameAddressTheSameField() {
 
    [Fact]
    public void DefaultValueAppliesWhenFieldNotGiven() {
-      var parser = new CommandLineParser<DifferentFieldNameArg>();
+      var parser = new CommandLineParser<DifferentFieldNameArg>(WithSlashPrefix);
 
       var result = parser.Parse(Args16);
 
@@ -258,7 +264,7 @@ public void DefaultValueAppliesWhenFieldNotGiven() {
 
    [Fact]
    public void RepeatedCollectionOption() {
-      var parser = new CommandLineParser<RealPrgArgs>();
+      var parser = new CommandLineParser<RealPrgArgs>(WithSlashPrefix);
 
       var result = parser.Parse(Args17);
 
@@ -270,7 +276,7 @@ public void RepeatedCollectionOption() {
 
    [Fact]
    public void CollectionWithSingleOptionAndSeveralValues() {
-      var parser = new CommandLineParser<RealPrgArgs>();
+      var parser = new CommandLineParser<RealPrgArgs>(WithSlashPrefix);
 
       var result = parser.Parse(Args18);
 
diff --git a/holonsoft.CmdLineParser.Tests/EdgeCaseTests.cs b/holonsoft.CmdLineParser.Tests/EdgeCaseTests.cs
index 6731a91..766f2a1 100644
--- a/holonsoft.CmdLineParser.Tests/EdgeCaseTests.cs
+++ b/holonsoft.CmdLineParser.Tests/EdgeCaseTests.cs
@@ -114,7 +114,7 @@ public class FormattedDefaults {
    [Theory]
    [InlineData("-Verbose:false", false)]
    [InlineData("-Verbose=yes", true)]
-   [InlineData("/v:0", false)]
+   [InlineData("-v:0", false)]
    public void InlineValueOnBool(string argument, bool expected) {
       var result = Parse(argument);
 
diff --git a/holonsoft.CmdLineParser.Tests/FuzzTests.cs b/holonsoft.CmdLineParser.Tests/FuzzTests.cs
index 6a57b16..c21f264 100644
--- a/holonsoft.CmdLineParser.Tests/FuzzTests.cs
+++ b/holonsoft.CmdLineParser.Tests/FuzzTests.cs
@@ -35,6 +35,9 @@ private static IEnumerable<Func<string[], object>> Parsers() {
       var relaxed = new CommandLineParser<HelpTests.Args>(new CommandLineParserOptions { IgnoreCase = true, AllowSlashPrefix = false, ValueSeparators = ['='] });
       yield return args => relaxed.ParseArguments(args);
 
+      var classic = new CommandLineParser<EdgeCaseTests.Args>(new CommandLineParserOptions { AllowSlashPrefix = true });
+      yield return args => classic.ParseArguments(args);
+
       var verbs = new VerbParser().Add<VerbParserTests.BuildArgs>().Add<VerbParserTests.TestArgs>().Add<VerbParserTests.RunArgs>("run", isDefault: true);
       yield return args => verbs.Parse(args);
    }
diff --git a/holonsoft.CmdLineParser.Tests/HelpTests.cs b/holonsoft.CmdLineParser.Tests/HelpTests.cs
index ca90213..358ad8b 100644
--- a/holonsoft.CmdLineParser.Tests/HelpTests.cs
+++ b/holonsoft.CmdLineParser.Tests/HelpTests.cs
@@ -121,7 +121,7 @@ public void WrapSplitsAtWordBoundaries() {
    [InlineData("/?")]
    [InlineData("-help")]
    public void BuiltInHelpSuppressesMissingRequiredErrors(string helpArgument) {
-      var result = new CommandLineParser<Args>().ParseArguments([helpArgument]);
+      var result = new CommandLineParser<Args>(new CommandLineParserOptions { AllowSlashPrefix = true }).ParseArguments([helpArgument]);
 
       Assert.True(result.HelpRequested);
       Assert.Empty(result.Errors);
diff --git a/holonsoft.CmdLineParser.Tests/ValidationTests.cs b/holonsoft.CmdLineParser.Tests/ValidationTests.cs
index 7007b88..6c2617d 100644
--- a/holonsoft.CmdLineParser.Tests/ValidationTests.cs
+++ b/holonsoft.CmdLineParser.Tests/ValidationTests.cs
@@ -242,8 +242,7 @@ public void MustExistChecksTheFileSystem() {
       var missing = Path.Combine(directory, Guid.NewGuid().ToString("N"));
 
       try {
-         // Absolute paths start with a slash on Unix, which the default options would read as an option prefix.
-         var parser = new CommandLineParser<ExistArgs>(new CommandLineParserOptions { AllowSlashPrefix = false });
+         var parser = new CommandLineParser<ExistArgs>();
 
          Assert.Empty(parser.ParseArguments(["-File", file, "-Directory", directory, "-Any", file]).Errors);
 
diff --git a/holonsoft.CmdLineParser.Tests/VerbParserTests.cs b/holonsoft.CmdLineParser.Tests/VerbParserTests.cs
index e0dbb2e..019aadd 100644
--- a/holonsoft.CmdLineParser.Tests/VerbParserTests.cs
+++ b/holonsoft.CmdLineParser.Tests/VerbParserTests.cs
@@ -93,7 +93,7 @@ public void DefaultVerbHandlesCommandLinesWithoutVerb() {
    [InlineData("-h")]
    [InlineData("/?")]
    public void HelpWithoutVerbAsksForTheOverview(string help) {
-      var result = Create().Parse([help]);
+      var result = new VerbParser(new CommandLineParserOptions { AllowSlashPrefix = true }).Add<BuildArgs>().Add<TestArgs>().Parse([help]);
 
       Assert.True(result.HelpRequested);
       Assert.Null(result.Verb);
diff --git a/holonsoft.CmdLineParser/CommandLineParserOptions.cs b/holonsoft.CmdLineParser/CommandLineParserOptions.cs
index 42b8dfb..7530e18 100644
--- a/holonsoft.CmdLineParser/CommandLineParserOptions.cs
+++ b/holonsoft.CmdLineParser/CommandLineParserOptions.cs
@@ -15,10 +15,11 @@ public sealed class CommandLineParserOptions {
    public bool IgnoreCase { get; set; }
 
    /// <summary>
-   /// Accept '/' as argument prefix in addition to '-' and '--'. Default: <c>true</c>.
-   /// Consider disabling this on Unix-like systems when values may be absolute paths.
+   /// Accept '/' as argument prefix in addition to '-' and '--', as in <c>/name</c> or <c>/?</c>.
+   /// Default: <c>true</c> on Windows, <c>false</c> elsewhere, because absolute paths start with '/' on Unix-like
+   /// systems and would otherwise be read as options. Set it explicitly when the behavior must not depend on the OS.
    /// </summary>
-   public bool AllowSlashPrefix { get; set; } = true;
+   public bool AllowSlashPrefix { get; set; } = OperatingSystem.IsWindows();
 
    /// <summary>
    /// Characters that separate an argument name from an inline value, as in <c>-name:value</c> or <c>--name=value</c>.