diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
new file mode 100644
index 0000000..61a5c03
--- /dev/null
+++ b/.github/copilot-instructions.md
@@ -0,0 +1,149 @@
+# AbstractPPL.jl
+
+AbstractPPL.jl is a Julia package that provides abstract interfaces and APIs for probabilistic programming languages. It defines core abstractions like `VarName` for variable names, `AbstractProbabilisticProgram` for probabilistic models, and utilities for managing traces and variable values.
+
+Always reference these instructions first and fallback to search or bash commands only when you encounter unexpected information that does not match the info here.
+
+## Working Effectively
+
+- Bootstrap, build, and test the repository:
+  - Julia is pre-installed (version 1.11.6)
+  - Navigate to the repository: `cd /home/runner/work/AbstractPPL.jl/AbstractPPL.jl`
+  - **Package instantiation**: `julia --project=. -e "using Pkg; Pkg.instantiate()"` -- takes 2-3 minutes on first run due to dependency downloads. NEVER CANCEL. Set timeout to 300+ seconds.
+  - **Main tests**: `julia --project=. -e "using Pkg; Pkg.test()"` -- takes 3 minutes including precompilation. NEVER CANCEL. Set timeout to 300+ seconds.
+  - **Tests only (skip precompilation)**: `julia --project=test -e "using Pkg; Pkg.develop(path=\".\"); ENV[\"GROUP\"] = \"Tests\"; include(\"test/runtests.jl\")"` -- takes 30 seconds. Set timeout to 60+ seconds.
+  - **Doctests only**: `julia --project=test -e "ENV[\"GROUP\"] = \"Doctests\"; include(\"test/runtests.jl\")"` -- takes 15 seconds. Set timeout to 60+ seconds.
+
+- Build documentation:
+  - Navigate to docs directory: `cd docs`  
+  - **Documentation build**: `julia --project=. -e "using Pkg; Pkg.instantiate(); include(\"make.jl\")"` -- takes 1-2 minutes. NEVER CANCEL. Set timeout to 180+ seconds.
+  - Documentation artifacts are created in `docs/build/`
+
+## Validation
+
+- **ALWAYS run the full test suite** before making any changes to understand baseline: `julia --project=. -e "using Pkg; Pkg.test()"`
+- **ALWAYS run formatting check** before committing: `julia --project=. -e "using Pkg; Pkg.add(\"JuliaFormatter\"); using JuliaFormatter; format(\".\", verbose=true)"` -- takes 1 minute. Set timeout to 120+ seconds.
+- **Code formatting** is enforced via CI. Check `.JuliaFormatter.toml` for style configuration.
+- **Manual validation scenarios**: Always test core functionality after making changes:
+  ```julia
+  julia --project=. -e "
+  using AbstractPPL
+  # Test VarName creation and introspection
+  vn = @varname x[1,2]
+  println(\"VarName: \", vn, \", Symbol: \", getsym(vn))
+  # Test hasvalue/getvalue with dictionaries
+  vals = Dict(@varname(x) => [1.0, 2.0, 3.0])
+  println(\"Has x: \", hasvalue(vals, @varname(x)))
+  println(\"Value: \", getvalue(vals, @varname(x)))
+  # Test VarName composition
+  vn2 = @varname y.a[1]
+  println(\"Composed VarName: \", vn2)
+  "
+  ```
+  Expected output should show VarName objects, successful value retrieval, and proper optic handling.
+- Test different GROUP environments: `Tests` for main tests, `Doctests` for documentation tests, or `All` for both
+- **Integration tests** exist for downstream packages like DynamicPPL.jl - these are run automatically in CI
+
+## Common Tasks
+
+The following commands are essential for working with this codebase:
+
+### Package Development Commands
+```bash
+# Install dependencies (NEVER CANCEL - 2-3 minutes)
+julia --project=. -e "using Pkg; Pkg.instantiate()"
+
+# Run full test suite (NEVER CANCEL - 3 minutes)  
+julia --project=. -e "using Pkg; Pkg.test()"
+
+# Run only main tests (30 seconds)
+julia --project=test -e "using Pkg; Pkg.develop(path=\".\"); ENV[\"GROUP\"] = \"Tests\"; include(\"test/runtests.jl\")"
+
+# Run only doctests (15 seconds)
+julia --project=test -e "ENV[\"GROUP\"] = \"Doctests\"; include(\"test/runtests.jl\")"
+
+# Format code (1 minute)
+julia --project=. -e "using Pkg; Pkg.add(\"JuliaFormatter\"); using JuliaFormatter; format(\".\", verbose=true)"
+
+# Build documentation (NEVER CANCEL - 1-2 minutes)
+cd docs && julia --project=. -e "using Pkg; Pkg.instantiate(); include(\"make.jl\")"
+```
+
+### Repository Structure
+```
+.
+├── .github/workflows/     # CI/CD workflows (CI, formatting, docs, integration tests)
+├── .JuliaFormatter.toml   # Code formatting configuration
+├── docs/                  # Documentation source and build
+├── ext/                   # Package extensions (DistributionsExt)
+├── src/                   # Main package source code
+├── test/                  # Test files and test dependencies
+├── Project.toml           # Main package dependencies
+└── README.md             # Package documentation
+```
+
+### Key Source Files
+- `src/AbstractPPL.jl` - Main module and exports
+- `src/varname.jl` - VarName implementation and utilities  
+- `src/abstractprobprog.jl` - AbstractProbabilisticProgram interface
+- `src/hasvalue.jl` - Functions for checking/extracting values from containers
+- `src/abstractmodeltrace.jl` - Abstract trace interface
+- `ext/AbstractPPLDistributionsExt.jl` - Extensions for working with Distributions.jl
+
+### Key Test Files  
+- `test/runtests.jl` - Main test runner (supports GROUP environment variable)
+- `test/varname.jl` - Tests for VarName functionality
+- `test/hasvalue.jl` - Tests for hasvalue/getvalue functions
+- `test/abstractprobprog.jl` - Tests for AbstractProbabilisticProgram interface
+
+## Timing Expectations
+
+**CRITICAL**: Set appropriate timeouts for all commands. DO NOT use default timeouts.
+
+- **Package instantiation**: 2-3 minutes (downloads dependencies) - Set timeout to 300+ seconds
+- **Full test suite**: 3 minutes (includes precompilation) - Set timeout to 300+ seconds  
+- **Main tests only**: 30 seconds - Set timeout to 60+ seconds
+- **Doctests only**: 15 seconds - Set timeout to 60+ seconds
+- **Code formatting**: 1 minute - Set timeout to 120+ seconds
+- **Documentation build**: 1-2 minutes - Set timeout to 180+ seconds
+
+**NEVER CANCEL** any of these operations. Julia package operations can appear to hang but are often downloading dependencies or precompiling.
+
+## Troubleshooting
+
+- **Network issues**: Julia package downloads may fail due to network restrictions. This is expected in CI environments.
+- **Precompilation warnings**: Various deprecation warnings during precompilation are normal and expected.
+- **Git warnings**: Documentation build may show git remote warnings - these are harmless.
+- **Test environment**: Some operations require using `--project=test` to access test dependencies like Documenter.jl.
+- **JuliaFormatter**: Must be added fresh each time with `Pkg.add("JuliaFormatter")` as it's not a permanent dependency.
+- **Package resolution warnings**: "could not download" warnings from pkg.julialang.org are expected in restricted environments.
+- **Manifest.toml changes**: Installing JuliaFormatter temporarily modifies Project.toml - always run `git checkout -- Project.toml` after formatting.
+
+## Performance Notes
+
+- **First run**: Package instantiation and first test run take longer due to compilation and downloads
+- **Subsequent runs**: Tests run faster (~25 seconds) when packages are already compiled
+- **Parallel testing**: The test suite runs tests in parallel, which is why it completes quickly
+- **Memory usage**: Julia precompilation can use significant memory - this is normal
+
+## CI/CD Information
+
+The repository uses GitHub Actions with these key workflows:
+- **CI.yml**: Runs tests on multiple Julia versions and platforms
+- **Format.yml**: Enforces code formatting with JuliaFormatter
+- **Docs.yml**: Builds and deploys documentation
+- **DocTests.yml**: Runs doctests separately  
+- **IntegrationTest.yml**: Tests against downstream packages (DynamicPPL.jl)
+
+Always run `julia --project=. -e "using JuliaFormatter; format(\".\")"` before committing to pass the Format.yml check.
+
+## Julia Package Development Concepts
+
+For developers new to Julia packages:
+- **Project.toml**: Defines package dependencies and metadata (like package.json or requirements.txt)
+- **Manifest.toml**: Lock file for exact dependency versions (automatically generated)
+- **--project=.**: Tells Julia to use the current directory's Project.toml environment
+- **--project=test**: Uses the test/ subdirectory environment with test-specific dependencies
+- **Package extensions**: Code in ext/ that's loaded only when optional dependencies are available (like DistributionsExt)
+- **using Pkg**: Julia's built-in package manager (like npm, pip, etc.)
+- **Precompilation**: Julia compiles packages on first use for faster subsequent loading
\ No newline at end of file
diff --git a/test/Project.toml b/test/Project.toml
index 23fb280..af9a4a1 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,4 +1,5 @@
 [deps]
+AbstractPPL = "7a57a42e-76ec-4ea3-a279-07e840d6d9cf"
 Accessors = "7d9f7c33-5ae7-4f3b-8dc6-eff91059b697"
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
diff --git a/test/varname.jl b/test/varname.jl
index 2fbff9b..278a1ba 100644
--- a/test/varname.jl
+++ b/test/varname.jl
@@ -245,8 +245,9 @@ end
             "parent" => AbstractPPL.index_to_dict(o.parent),
             "offset" => o.offset,
         )
-        AbstractPPL.dict_to_index(::Val{Symbol("OffsetArrays.OffsetArray")}, d) =
-            OffsetArrays.IdOffsetRange(AbstractPPL.dict_to_index(d["parent"]), d["offset"])
+        AbstractPPL.dict_to_index(::Val{Symbol("OffsetArrays.OffsetArray")}, d) = OffsetArrays.IdOffsetRange(
+            AbstractPPL.dict_to_index(d["parent"]), d["offset"]
+        )
 
         # Serialisation should now work
         @test string_to_varname(varname_to_string(vn)) == vn