diff --git a/assets/examples/60_custom_math.iesopt.yaml b/assets/examples/60_custom_math.iesopt.yaml
new file mode 100644
index 0000000..23e4617
--- /dev/null
+++ b/assets/examples/60_custom_math.iesopt.yaml
@@ -0,0 +1,41 @@
+config:
+  general:
+    version:
+      core: 2.6.3
+  optimization:
+    problem_type: MILP
+    snapshots:
+      count: 9
+    solver:
+      name: highs
+  paths:
+    addons: files/60
+
+addons:
+  CustomMath: {}
+
+carriers:
+  electricity: {}
+  gas: {}
+
+components:
+  grid_electricity:
+    type: Node
+    carrier: electricity
+
+  grid_gas:
+    type: Node
+    carrier: gas
+
+  demand_elec:
+    type: Profile
+    carrier: electricity
+    node_from: grid_electricity
+    value: [2.75,  5.50,  7.00,  8.00,  9.00, 10.00, 5.00, 5.00, 15.00]
+
+  create_gas:
+    type: Profile
+    carrier: gas
+    node_to: grid_gas
+    mode: create
+    cost: 50.0
diff --git a/assets/examples/files/60/CustomMath.jl b/assets/examples/files/60/CustomMath.jl
new file mode 100644
index 0000000..9cb24b5
--- /dev/null
+++ b/assets/examples/files/60/CustomMath.jl
@@ -0,0 +1,45 @@
+module IESoptAddon_CustomMath
+
+using IESopt
+import JuMP
+
+function initialize!(model::JuMP.Model, config::Dict)
+    # All functions are expected to return `true` if everything went well.
+    return true
+end
+
+# The following functions are called after they were called for all core components:
+# - setup!
+# - construct_expressions!
+# - construct_variables!
+# - construct_constraints!
+# - construct_objective!
+#
+# If you do not need to modify the model during a specific step, you can just not implement the function.
+
+function construct_variables!(model::JuMP.Model, config::Dict)
+    T = get_T(model)
+
+    node_input = get_component(model, "grid_gas")
+    node_output = get_component(model, "grid_electricity")
+
+    JuMP.@variable(model, var_input[t in T], lower_bound=0.0)
+    # NOTE: This is just a weird example of the possibility to attach new things.
+    node_output.exp.generation = 1.1 .* JuMP.@variable(model, var_output[t in T], lower_bound=0.0, container=Array)
+
+    JuMP.@constraint(
+        model,
+        [t in T],
+        # NOTE: This could be a more complex mathematical expression, e.g., a piecewise interpolation.
+        node_output.exp.generation[t] == 0.5 * model[:var_input][t]
+    )
+
+    for t in T
+        JuMP.add_to_expression!(node_input.exp.injection[t], model[:var_input][t], -1.0)
+        JuMP.add_to_expression!(node_output.exp.injection[t], node_output.exp.generation[t], 1.0)
+    end
+
+    return true
+end
+
+end
diff --git a/test/src/examples.jl b/test/src/examples.jl
index 6865916..600bdf2 100644
--- a/test/src/examples.jl
+++ b/test/src/examples.jl
@@ -363,3 +363,14 @@ end
         @test JuMP.value(get_component(model, "grid_tariff_power_consumption_$m").var.value) ≈ check[m] atol = 1e-4
     end
 end
+
+@testitem "60_custom_math" tags = [:examples] setup = [Dependencies, TestExampleModule] begin
+    model = TestExampleModule.check(; obj=6725.0)
+
+    check = [2.75, 5.5, 7.0, 8.0, 9.0, 10.0, 5.0, 5.0, 15.0]
+    vin = JuMP.value.(model[:var_input])
+    vout = JuMP.value.(get_component(model, "grid_electricity").exp.generation)
+    
+    @test all(vin .≈ 2.0 .* check)
+    @test all(vout .≈ check)
+end