diff --git a/docs/src/basics/AbstractSystem.md b/docs/src/basics/AbstractSystem.md
index 2161613353..e68a7bb94e 100644
--- a/docs/src/basics/AbstractSystem.md
+++ b/docs/src/basics/AbstractSystem.md
@@ -63,6 +63,7 @@ Optionally, a system could have:
   - `get_defaults(sys)`: A `Dict` that maps variables into their default values
     for the current-level system.
   - `get_noiseeqs(sys)`: Noise equations of the current-level system.
+  - `get_description(sys)`: A string that describes what a system represents.
   - `get_metadata(sys)`: Any metadata about the system or its origin to be used by downstream packages.
 
 Note that if you know a system is an `AbstractTimeDependentSystem` you could use `get_iv` to get the
diff --git a/src/ModelingToolkit.jl b/src/ModelingToolkit.jl
index 2f57bb1765..7687122a61 100644
--- a/src/ModelingToolkit.jl
+++ b/src/ModelingToolkit.jl
@@ -243,7 +243,7 @@ export Equation, ConstrainedEquation
 export Term, Sym
 export SymScope, LocalScope, ParentScope, DelayParentScope, GlobalScope
 export independent_variable, equations, controls, observed, full_equations
-export initialization_equations, guesses, defaults, parameter_dependencies
+export initialization_equations, guesses, defaults, parameter_dependencies, hierarchy
 export structural_simplify, expand_connections, linearize, linearization_function
 
 export calculate_jacobian, generate_jacobian, generate_function, generate_custom_function
diff --git a/src/systems/abstractsystem.jl b/src/systems/abstractsystem.jl
index b6e2a79c3e..226c4ff55d 100644
--- a/src/systems/abstractsystem.jl
+++ b/src/systems/abstractsystem.jl
@@ -498,6 +498,7 @@ end
 Substitutions(subs, deps) = Substitutions(subs, deps, nothing)
 
 Base.nameof(sys::AbstractSystem) = getfield(sys, :name)
+description(sys::AbstractSystem) = has_description(sys) ? get_description(sys) : ""
 
 #Deprecated
 function independent_variable(sys::AbstractSystem)
@@ -986,6 +987,7 @@ for prop in [:eqs
              :ps
              :tspan
              :name
+             :description
              :var_to_name
              :ctrls
              :defaults
@@ -1855,8 +1857,14 @@ function get_or_construct_tearing_state(sys)
     state
 end
 
-# TODO: what about inputs?
-function n_extra_equations(sys::AbstractSystem)
+"""
+    n_expanded_connection_equations(sys::AbstractSystem)
+
+Returns the number of equations that the connections in `sys` expands to.
+Equivalent to `length(equations(expand_connections(sys))) - length(filter(eq -> !(eq.lhs isa Connection), equations(sys)))`.
+"""
+function n_expanded_connection_equations(sys::AbstractSystem)
+    # TODO: what about inputs?
     isconnector(sys) && return length(get_unknowns(sys))
     sys, (csets, _) = generate_connection_set(sys)
     ceqs, instream_csets = generate_connection_equations_and_stream_connections(csets)
@@ -1883,84 +1891,89 @@ function n_extra_equations(sys::AbstractSystem)
     nextras = n_outer_stream_variables + length(ceqs)
 end
 
-function Base.show(io::IO, mime::MIME"text/plain", sys::AbstractSystem)
-    eqs = equations(sys)
-    vars = unknowns(sys)
-    nvars = length(vars)
-    if eqs isa AbstractArray && eltype(eqs) <: Equation
-        neqs = count(eq -> !(eq.lhs isa Connection), eqs)
-        Base.printstyled(io, "Model $(nameof(sys)) with $neqs "; bold = true)
-        nextras = n_extra_equations(sys)
-        if nextras > 0
-            Base.printstyled(io, "("; bold = true)
-            Base.printstyled(io, neqs + nextras; bold = true, color = :magenta)
-            Base.printstyled(io, ") "; bold = true)
-        end
-        Base.printstyled(io, "equations\n"; bold = true)
-    else
-        Base.printstyled(io, "Model $(nameof(sys))\n"; bold = true)
-    end
-    # The reduced equations are usually very long. It's not that useful to print
-    # them.
-    #Base.print_matrix(io, eqs)
-    #println(io)
+function Base.show(
+        io::IO, mime::MIME"text/plain", sys::AbstractSystem; hint = true, bold = true)
+    limit = get(io, :limit, false) # if output should be limited,
+    rows = first(displaysize(io)) ÷ 5 # then allocate ≈1/5 of display height to each list
 
-    rows = first(displaysize(io)) ÷ 5
-    limit = get(io, :limit, false)
+    # Print name and description
+    desc = description(sys)
+    printstyled(io, "Model ", nameof(sys), ":"; bold)
+    !isempty(desc) && print(io, " ", desc)
 
-    Base.printstyled(io, "Unknowns ($nvars):"; bold = true)
-    nrows = min(nvars, limit ? rows : nvars)
-    limited = nrows < length(vars)
-    defs = has_defaults(sys) ? defaults(sys) : nothing
+    # Print subsystems
+    subs = get_systems(sys)
+    nsubs = length(subs)
+    nrows = min(nsubs, limit ? rows : nsubs)
+    nrows > 0 && printstyled(io, "\nSubsystems ($(nsubs)):"; bold)
+    nrows > 0 && hint && print(io, " see hierarchy(sys)")
     for i in 1:nrows
-        s = vars[i]
-        print(io, "\n  ", s)
-
-        if defs !== nothing
-            val = get(defs, s, nothing)
-            if val !== nothing
-                print(io, " [defaults to ")
-                show(
-                    IOContext(io, :compact => true, :limit => true,
-                        :displaysize => (1, displaysize(io)[2])),
-                    val)
-                print(io, "]")
-            end
-            description = getdescription(s)
-            if description !== nothing && description != ""
-                print(io, ": ", description)
+        sub = subs[i]
+        name = String(nameof(sub))
+        print(io, "\n  ", name)
+        desc = description(sub)
+        if !isempty(desc)
+            maxlen = displaysize(io)[2] - length(name) - 6 # remaining length of line
+            if limit && length(desc) > maxlen
+                desc = chop(desc, tail = length(desc) - maxlen) * "…" # too long
             end
+            print(io, ": ", desc)
         end
     end
-    limited && print(io, "\n⋮")
-    println(io)
+    limited = nrows < nsubs
+    limited && print(io, "\n  ⋮") # too many to print 
 
-    vars = parameters(sys)
-    nvars = length(vars)
-    Base.printstyled(io, "Parameters ($nvars):"; bold = true)
-    nrows = min(nvars, limit ? rows : nvars)
-    limited = nrows < length(vars)
-    for i in 1:nrows
-        s = vars[i]
-        print(io, "\n  ", s)
-
-        if defs !== nothing
-            val = get(defs, s, nothing)
-            if val !== nothing
-                print(io, " [defaults to ")
-                show(
-                    IOContext(io, :compact => true, :limit => true,
-                        :displaysize => (1, displaysize(io)[2])),
-                    val)
-                print(io, "]")
+    # Print equations
+    eqs = equations(sys)
+    if eqs isa AbstractArray && eltype(eqs) <: Equation
+        neqs = count(eq -> !(eq.lhs isa Connection), eqs)
+        next = n_expanded_connection_equations(sys)
+        ntot = neqs + next
+        ntot > 0 && printstyled(io, "\nEquations ($ntot):"; bold)
+        neqs > 0 && print(io, "\n  $neqs standard", hint ? ": see equations(sys)" : "")
+        next > 0 && print(io, "\n  $next connecting",
+            hint ? ": see equations(expand_connections(sys))" : "")
+        #Base.print_matrix(io, eqs) # usually too long and not useful to print all equations
+    end
+
+    # Print variables
+    for varfunc in [unknowns, parameters]
+        vars = varfunc(sys)
+        nvars = length(vars)
+        nvars == 0 && continue # skip
+        header = titlecase(String(nameof(varfunc))) # e.g. "Unknowns"
+        printstyled(io, "\n$header ($nvars):"; bold)
+        hint && print(io, " see $(nameof(varfunc))(sys)")
+        nrows = min(nvars, limit ? rows : nvars)
+        defs = has_defaults(sys) ? defaults(sys) : nothing
+        for i in 1:nrows
+            s = vars[i]
+            print(io, "\n  ", s)
+            if !isnothing(defs)
+                val = get(defs, s, nothing)
+                if !isnothing(val)
+                    print(io, " [defaults to ")
+                    show(
+                        IOContext(io, :compact => true, :limit => true,
+                            :displaysize => (1, displaysize(io)[2])),
+                        val)
+                    print(io, "]")
+                end
+                desc = getdescription(s)
             end
-            description = getdescription(s)
-            if description !== nothing && description != ""
-                print(io, ": ", description)
+            if !isnothing(desc) && desc != ""
+                print(io, ": ", desc)
             end
         end
+        limited = nrows < nvars
+        limited && printstyled(io, "\n  ⋮") # too many variables to print
     end
-    limited && print(io, "\n⋮")
+
+    # Print observed
+    nobs = has_observed(sys) ? length(observed(sys)) : 0
+    nobs > 0 && printstyled(io, "\nObserved ($nobs):"; bold)
+    nobs > 0 && hint && print(io, " see observed(sys)")
+
     return nothing
 end
 
@@ -2900,12 +2913,23 @@ function Base.showerror(io::IO, e::HybridSystemNotSupportedException)
     print(io, "HybridSystemNotSupportedException: ", e.msg)
 end
 
-function AbstractTrees.children(sys::ModelingToolkit.AbstractSystem)
+function AbstractTrees.children(sys::AbstractSystem)
     ModelingToolkit.get_systems(sys)
 end
-function AbstractTrees.printnode(io::IO, sys::ModelingToolkit.AbstractSystem)
-    print(io, nameof(sys))
+function AbstractTrees.printnode(
+        io::IO, sys::AbstractSystem; describe = false, bold = false)
+    printstyled(io, nameof(sys); bold)
+    describe && !isempty(description(sys)) && print(io, ": ", description(sys))
 end
+"""
+    hierarchy(sys::AbstractSystem; describe = false, bold = describe, kwargs...)
+
+Print a tree of a system's hierarchy of subsystems.
+"""
+function hierarchy(sys::AbstractSystem; describe = false, bold = describe, kwargs...)
+    print_tree(sys; printnode_kw = (describe = describe, bold = bold), kwargs...)
+end
+
 function Base.IteratorEltype(::Type{<:TreeIterator{ModelingToolkit.AbstractSystem}})
     Base.HasEltype()
 end
@@ -2988,12 +3012,13 @@ function extend(sys::AbstractSystem, basesys::AbstractSystem; name::Symbol = nam
     cevs = union(get_continuous_events(basesys), get_continuous_events(sys))
     devs = union(get_discrete_events(basesys), get_discrete_events(sys))
     defs = merge(get_defaults(basesys), get_defaults(sys)) # prefer `sys`
+    desc = join(filter(desc -> !isempty(desc), description.([sys, basesys])), " ") # concatenate non-empty descriptions with space
     meta = union_nothing(get_metadata(basesys), get_metadata(sys))
     syss = union(get_systems(basesys), get_systems(sys))
     args = length(ivs) == 0 ? (eqs, sts, ps) : (eqs, ivs[1], sts, ps)
     kwargs = (parameter_dependencies = dep_ps, observed = obs, continuous_events = cevs,
         discrete_events = devs, defaults = defs, systems = syss, metadata = meta,
-        name = name, gui_metadata = gui_metadata)
+        name = name, description = desc, gui_metadata = gui_metadata)
 
     # collect fields specific to some system types
     if basesys isa ODESystem
diff --git a/src/systems/diffeqs/odesystem.jl b/src/systems/diffeqs/odesystem.jl
index ec2c5f8157..2176e53d55 100644
--- a/src/systems/diffeqs/odesystem.jl
+++ b/src/systems/diffeqs/odesystem.jl
@@ -79,6 +79,10 @@ struct ODESystem <: AbstractODESystem
     """
     name::Symbol
     """
+    A description of the system.
+    """
+    description::String
+    """
     The internal systems. These are required to have unique names.
     """
     systems::Vector{ODESystem}
@@ -178,7 +182,7 @@ struct ODESystem <: AbstractODESystem
     parent::Any
 
     function ODESystem(tag, deqs, iv, dvs, ps, tspan, var_to_name, ctrls, observed, tgrad,
-            jac, ctrl_jac, Wfact, Wfact_t, name, systems, defaults, guesses,
+            jac, ctrl_jac, Wfact, Wfact_t, name, description, systems, defaults, guesses,
             torn_matching, initializesystem, initialization_eqs, schedule,
             connector_type, preface, cevents,
             devents, parameter_dependencies,
@@ -199,7 +203,7 @@ struct ODESystem <: AbstractODESystem
             check_units(u, deqs)
         end
         new(tag, deqs, iv, dvs, ps, tspan, var_to_name, ctrls, observed, tgrad, jac,
-            ctrl_jac, Wfact, Wfact_t, name, systems, defaults, guesses, torn_matching,
+            ctrl_jac, Wfact, Wfact_t, name, description, systems, defaults, guesses, torn_matching,
             initializesystem, initialization_eqs, schedule, connector_type, preface,
             cevents, devents, parameter_dependencies, metadata,
             gui_metadata, is_dde, tearing_state, substitutions, complete, index_cache,
@@ -213,6 +217,7 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
         systems = ODESystem[],
         tspan = nothing,
         name = nothing,
+        description = "",
         default_u0 = Dict(),
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
@@ -290,7 +295,8 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
     end
     ODESystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
         deqs, iv′, dvs′, ps′, tspan, var_to_name, ctrl′, observed, tgrad, jac,
-        ctrl_jac, Wfact, Wfact_t, name, systems, defaults, guesses, nothing, initializesystem,
+        ctrl_jac, Wfact, Wfact_t, name, description, systems,
+        defaults, guesses, nothing, initializesystem,
         initialization_eqs, schedule, connector_type, preface, cont_callbacks,
         disc_callbacks, parameter_dependencies,
         metadata, gui_metadata, is_dde, checks = checks)
@@ -393,6 +399,7 @@ function flatten(sys::ODESystem, noeqs = false)
             discrete_events = discrete_events(sys),
             defaults = defaults(sys),
             name = nameof(sys),
+            description = description(sys),
             initialization_eqs = initialization_equations(sys),
             is_dde = is_dde(sys),
             checks = false)
@@ -697,3 +704,16 @@ function add_accumulations(sys::ODESystem, vars::Vector{<:Pair})
     @set! sys.unknowns = [get_unknowns(sys); avars]
     @set! sys.defaults = merge(get_defaults(sys), Dict(a => 0.0 for a in avars))
 end
+
+function Base.show(io::IO, mime::MIME"text/plain", sys::ODESystem; hint = true, bold = true)
+    # Print general AbstractSystem information
+    invoke(Base.show, Tuple{typeof(io), typeof(mime), AbstractSystem},
+        io, mime, sys; hint, bold)
+
+    # Print initialization equations (unique to ODESystems)
+    nini = length(initialization_equations(sys))
+    nini > 0 && printstyled(io, "\nInitialization equations ($nini):"; bold)
+    nini > 0 && hint && print(io, " see initialization_equations(sys)")
+
+    return nothing
+end
diff --git a/src/systems/diffeqs/sdesystem.jl b/src/systems/diffeqs/sdesystem.jl
index 0d73aaf313..9f3814774f 100644
--- a/src/systems/diffeqs/sdesystem.jl
+++ b/src/systems/diffeqs/sdesystem.jl
@@ -80,6 +80,10 @@ struct SDESystem <: AbstractODESystem
     """
     name::Symbol
     """
+    A description of the system.
+    """
+    description::String
+    """
     The internal systems. These are required to have unique names.
     """
     systems::Vector{SDESystem}
@@ -142,7 +146,7 @@ struct SDESystem <: AbstractODESystem
     function SDESystem(tag, deqs, neqs, iv, dvs, ps, tspan, var_to_name, ctrls, observed,
             tgrad,
             jac,
-            ctrl_jac, Wfact, Wfact_t, name, systems, defaults, connector_type,
+            ctrl_jac, Wfact, Wfact_t, name, description, systems, defaults, connector_type,
             cevents, devents, parameter_dependencies, metadata = nothing, gui_metadata = nothing,
             complete = false, index_cache = nothing, parent = nothing, is_scalar_noise = false,
             is_dde = false,
@@ -168,7 +172,8 @@ struct SDESystem <: AbstractODESystem
         end
         new(tag, deqs, neqs, iv, dvs, ps, tspan, var_to_name, ctrls, observed, tgrad, jac,
             ctrl_jac,
-            Wfact, Wfact_t, name, systems, defaults, connector_type, cevents, devents,
+            Wfact, Wfact_t, name, description, systems,
+            defaults, connector_type, cevents, devents,
             parameter_dependencies, metadata, gui_metadata, complete, index_cache, parent, is_scalar_noise,
             is_dde, isscheduled)
     end
@@ -183,6 +188,7 @@ function SDESystem(deqs::AbstractVector{<:Equation}, neqs::AbstractArray, iv, dv
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
         name = nothing,
+        description = "",
         connector_type = nothing,
         checks = true,
         continuous_events = nothing,
@@ -234,7 +240,7 @@ function SDESystem(deqs::AbstractVector{<:Equation}, neqs::AbstractArray, iv, dv
     end
     SDESystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
         deqs, neqs, iv′, dvs′, ps′, tspan, var_to_name, ctrl′, observed, tgrad, jac,
-        ctrl_jac, Wfact, Wfact_t, name, systems, defaults, connector_type,
+        ctrl_jac, Wfact, Wfact_t, name, description, systems, defaults, connector_type,
         cont_callbacks, disc_callbacks, parameter_dependencies, metadata, gui_metadata,
         complete, index_cache, parent, is_scalar_noise, is_dde; checks = checks)
 end
@@ -349,7 +355,8 @@ function stochastic_integral_transform(sys::SDESystem, correction_factor)
     end
 
     SDESystem(deqs, get_noiseeqs(sys), get_iv(sys), unknowns(sys), parameters(sys),
-        name = name, parameter_dependencies = parameter_dependencies(sys), checks = false)
+        name = name, description = description(sys),
+        parameter_dependencies = parameter_dependencies(sys), checks = false)
 end
 
 """
@@ -457,7 +464,8 @@ function Girsanov_transform(sys::SDESystem, u; θ0 = 1.0)
     # return modified SDE System
     SDESystem(deqs, noiseeqs, get_iv(sys), unknown_vars, parameters(sys);
         defaults = Dict(θ => θ0), observed = [weight ~ θ / θ0],
-        name = name, parameter_dependencies = parameter_dependencies(sys),
+        name = name, description = description(sys),
+        parameter_dependencies = parameter_dependencies(sys),
         checks = false)
 end
 
diff --git a/src/systems/discrete_system/discrete_system.jl b/src/systems/discrete_system/discrete_system.jl
index b09ecf5c4c..3e220998cb 100644
--- a/src/systems/discrete_system/discrete_system.jl
+++ b/src/systems/discrete_system/discrete_system.jl
@@ -42,6 +42,10 @@ struct DiscreteSystem <: AbstractTimeDependentSystem
     """
     name::Symbol
     """
+    A description of the system.
+    """
+    description::String
+    """
     The internal systems. These are required to have unique names.
     """
     systems::Vector{DiscreteSystem}
@@ -95,7 +99,7 @@ struct DiscreteSystem <: AbstractTimeDependentSystem
 
     function DiscreteSystem(tag, discreteEqs, iv, dvs, ps, tspan, var_to_name,
             observed,
-            name,
+            name, description,
             systems, defaults, preface, connector_type, parameter_dependencies = Equation[],
             metadata = nothing, gui_metadata = nothing,
             tearing_state = nothing, substitutions = nothing,
@@ -111,7 +115,7 @@ struct DiscreteSystem <: AbstractTimeDependentSystem
             u = __get_unit_type(dvs, ps, iv)
             check_units(u, discreteEqs)
         end
-        new(tag, discreteEqs, iv, dvs, ps, tspan, var_to_name, observed, name,
+        new(tag, discreteEqs, iv, dvs, ps, tspan, var_to_name, observed, name, description,
             systems,
             defaults,
             preface, connector_type, parameter_dependencies, metadata, gui_metadata,
@@ -128,6 +132,7 @@ function DiscreteSystem(eqs::AbstractVector{<:Equation}, iv, dvs, ps;
         systems = DiscreteSystem[],
         tspan = nothing,
         name = nothing,
+        description = "",
         default_u0 = Dict(),
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
@@ -164,7 +169,7 @@ function DiscreteSystem(eqs::AbstractVector{<:Equation}, iv, dvs, ps;
         throw(ArgumentError("System names must be unique."))
     end
     DiscreteSystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
-        eqs, iv′, dvs′, ps′, tspan, var_to_name, observed, name, systems,
+        eqs, iv′, dvs′, ps′, tspan, var_to_name, observed, name, description, systems,
         defaults, preface, connector_type, parameter_dependencies, metadata, gui_metadata, kwargs...)
 end
 
@@ -221,6 +226,7 @@ function flatten(sys::DiscreteSystem, noeqs = false)
             observed = observed(sys),
             defaults = defaults(sys),
             name = nameof(sys),
+            description = description(sys),
             checks = false)
     end
 end
diff --git a/src/systems/jumps/jumpsystem.jl b/src/systems/jumps/jumpsystem.jl
index a714d4b364..6409609a10 100644
--- a/src/systems/jumps/jumpsystem.jl
+++ b/src/systems/jumps/jumpsystem.jl
@@ -74,6 +74,8 @@ struct JumpSystem{U <: ArrayPartition} <: AbstractTimeDependentSystem
     observed::Vector{Equation}
     """The name of the system."""
     name::Symbol
+    """A description of the system."""
+    description::String
     """The internal systems. These are required to have unique names."""
     systems::Vector{JumpSystem}
     """
@@ -116,7 +118,8 @@ struct JumpSystem{U <: ArrayPartition} <: AbstractTimeDependentSystem
     index_cache::Union{Nothing, IndexCache}
     isscheduled::Bool
 
-    function JumpSystem{U}(tag, ap::U, iv, unknowns, ps, var_to_name, observed, name,
+    function JumpSystem{U}(
+            tag, ap::U, iv, unknowns, ps, var_to_name, observed, name, description,
             systems,
             defaults, connector_type, devents, parameter_dependencies,
             metadata = nothing, gui_metadata = nothing,
@@ -131,7 +134,8 @@ struct JumpSystem{U <: ArrayPartition} <: AbstractTimeDependentSystem
             u = __get_unit_type(unknowns, ps, iv)
             check_units(u, ap, iv)
         end
-        new{U}(tag, ap, iv, unknowns, ps, var_to_name, observed, name, systems, defaults,
+        new{U}(tag, ap, iv, unknowns, ps, var_to_name,
+            observed, name, description, systems, defaults,
             connector_type, devents, parameter_dependencies, metadata, gui_metadata,
             complete, index_cache, isscheduled)
     end
@@ -147,6 +151,7 @@ function JumpSystem(eqs, iv, unknowns, ps;
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
         name = nothing,
+        description = "",
         connector_type = nothing,
         checks = true,
         continuous_events = nothing,
@@ -193,7 +198,7 @@ function JumpSystem(eqs, iv, unknowns, ps;
     disc_callbacks = SymbolicDiscreteCallbacks(discrete_events)
     parameter_dependencies, ps = process_parameter_dependencies(parameter_dependencies, ps)
     JumpSystem{typeof(ap)}(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
-        ap, value(iv), unknowns, ps, var_to_name, observed, name, systems,
+        ap, value(iv), unknowns, ps, var_to_name, observed, name, description, systems,
         defaults, connector_type, disc_callbacks, parameter_dependencies,
         metadata, gui_metadata, checks = checks)
 end
diff --git a/src/systems/nonlinear/nonlinearsystem.jl b/src/systems/nonlinear/nonlinearsystem.jl
index d9ad826a2c..3b0e4b7e92 100644
--- a/src/systems/nonlinear/nonlinearsystem.jl
+++ b/src/systems/nonlinear/nonlinearsystem.jl
@@ -44,6 +44,10 @@ struct NonlinearSystem <: AbstractTimeIndependentSystem
     """
     name::Symbol
     """
+    A description of the system.
+    """
+    description::String
+    """
     The internal systems. These are required to have unique names.
     """
     systems::Vector{NonlinearSystem}
@@ -91,7 +95,8 @@ struct NonlinearSystem <: AbstractTimeIndependentSystem
     parent::Any
     isscheduled::Bool
 
-    function NonlinearSystem(tag, eqs, unknowns, ps, var_to_name, observed, jac, name,
+    function NonlinearSystem(
+            tag, eqs, unknowns, ps, var_to_name, observed, jac, name, description,
             systems,
             defaults, connector_type, parameter_dependencies = Equation[], metadata = nothing,
             gui_metadata = nothing,
@@ -102,7 +107,8 @@ struct NonlinearSystem <: AbstractTimeIndependentSystem
             u = __get_unit_type(unknowns, ps)
             check_units(u, eqs)
         end
-        new(tag, eqs, unknowns, ps, var_to_name, observed, jac, name, systems, defaults,
+        new(tag, eqs, unknowns, ps, var_to_name, observed,
+            jac, name, description, systems, defaults,
             connector_type, parameter_dependencies, metadata, gui_metadata, tearing_state,
             substitutions, complete, index_cache, parent, isscheduled)
     end
@@ -111,6 +117,7 @@ end
 function NonlinearSystem(eqs, unknowns, ps;
         observed = [],
         name = nothing,
+        description = "",
         default_u0 = Dict(),
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
@@ -157,7 +164,7 @@ function NonlinearSystem(eqs, unknowns, ps;
     parameter_dependencies, ps = process_parameter_dependencies(
         parameter_dependencies, ps)
     NonlinearSystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
-        eqs, unknowns, ps, var_to_name, observed, jac, name, systems, defaults,
+        eqs, unknowns, ps, var_to_name, observed, jac, name, description, systems, defaults,
         connector_type, parameter_dependencies, metadata, gui_metadata, checks = checks)
 end
 
@@ -554,6 +561,7 @@ function flatten(sys::NonlinearSystem, noeqs = false)
             observed = observed(sys),
             defaults = defaults(sys),
             name = nameof(sys),
+            description = description(sys),
             checks = false)
     end
 end
diff --git a/src/systems/optimization/constraints_system.jl b/src/systems/optimization/constraints_system.jl
index f9176df3a2..a2756994ac 100644
--- a/src/systems/optimization/constraints_system.jl
+++ b/src/systems/optimization/constraints_system.jl
@@ -45,6 +45,10 @@ struct ConstraintsSystem <: AbstractTimeIndependentSystem
     """
     name::Symbol
     """
+    A description of the system.
+    """
+    description::String
+    """
     The internal systems. These are required to have unique names.
     """
     systems::Vector{ConstraintsSystem}
@@ -79,7 +83,7 @@ struct ConstraintsSystem <: AbstractTimeIndependentSystem
     index_cache::Union{Nothing, IndexCache}
 
     function ConstraintsSystem(tag, constraints, unknowns, ps, var_to_name, observed, jac,
-            name,
+            name, description,
             systems,
             defaults, connector_type, metadata = nothing,
             tearing_state = nothing, substitutions = nothing,
@@ -89,7 +93,8 @@ struct ConstraintsSystem <: AbstractTimeIndependentSystem
             u = __get_unit_type(unknowns, ps)
             check_units(u, constraints)
         end
-        new(tag, constraints, unknowns, ps, var_to_name, observed, jac, name, systems,
+        new(tag, constraints, unknowns, ps, var_to_name,
+            observed, jac, name, description, systems,
             defaults,
             connector_type, metadata, tearing_state, substitutions, complete, index_cache)
     end
@@ -100,6 +105,7 @@ equations(sys::ConstraintsSystem) = constraints(sys) # needed for Base.show
 function ConstraintsSystem(constraints, unknowns, ps;
         observed = [],
         name = nothing,
+        description = "",
         default_u0 = Dict(),
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
@@ -142,7 +148,7 @@ function ConstraintsSystem(constraints, unknowns, ps;
     isempty(observed) || collect_var_to_name!(var_to_name, (eq.lhs for eq in observed))
 
     ConstraintsSystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
-        cstr, unknowns, ps, var_to_name, observed, jac, name, systems,
+        cstr, unknowns, ps, var_to_name, observed, jac, name, description, systems,
         defaults,
         connector_type, metadata, checks = checks)
 end
diff --git a/src/systems/optimization/optimizationsystem.jl b/src/systems/optimization/optimizationsystem.jl
index 22488e8bad..1f543dc8d1 100644
--- a/src/systems/optimization/optimizationsystem.jl
+++ b/src/systems/optimization/optimizationsystem.jl
@@ -37,6 +37,8 @@ struct OptimizationSystem <: AbstractOptimizationSystem
     constraints::Vector{Union{Equation, Inequality}}
     """The name of the system."""
     name::Symbol
+    """A description of the system."""
+    description::String
     """The internal systems. These are required to have unique names."""
     systems::Vector{OptimizationSystem}
     """
@@ -67,7 +69,7 @@ struct OptimizationSystem <: AbstractOptimizationSystem
     isscheduled::Bool
 
     function OptimizationSystem(tag, op, unknowns, ps, var_to_name, observed,
-            constraints, name, systems, defaults, metadata = nothing,
+            constraints, name, description, systems, defaults, metadata = nothing,
             gui_metadata = nothing, complete = false, index_cache = nothing, parent = nothing,
             isscheduled = false;
             checks::Union{Bool, Int} = true)
@@ -78,7 +80,7 @@ struct OptimizationSystem <: AbstractOptimizationSystem
             check_units(u, constraints)
         end
         new(tag, op, unknowns, ps, var_to_name, observed,
-            constraints, name, systems, defaults, metadata, gui_metadata, complete,
+            constraints, name, description, systems, defaults, metadata, gui_metadata, complete,
             index_cache, parent, isscheduled)
     end
 end
@@ -92,6 +94,7 @@ function OptimizationSystem(op, unknowns, ps;
         default_p = Dict(),
         defaults = _merge(Dict(default_u0), Dict(default_p)),
         name = nothing,
+        description = "",
         systems = OptimizationSystem[],
         checks = true,
         metadata = nothing,
@@ -125,7 +128,7 @@ function OptimizationSystem(op, unknowns, ps;
         op′, unknowns′, ps′, var_to_name,
         observed,
         constraints,
-        name, systems, defaults, metadata, gui_metadata;
+        name, description, systems, defaults, metadata, gui_metadata;
         checks = checks)
 end
 
diff --git a/src/systems/pde/pdesystem.jl b/src/systems/pde/pdesystem.jl
index 7aa3f29191..eac540e401 100644
--- a/src/systems/pde/pdesystem.jl
+++ b/src/systems/pde/pdesystem.jl
@@ -78,6 +78,10 @@ struct PDESystem <: ModelingToolkit.AbstractMultivariateSystem
     """
     name::Symbol
     """
+    A description of the system.
+    """
+    description::String
+    """
     Metadata for the system, to be used by downstream packages.
     """
     metadata::Any
@@ -96,6 +100,7 @@ struct PDESystem <: ModelingToolkit.AbstractMultivariateSystem
             gui_metadata = nothing,
             eval_module = @__MODULE__,
             checks::Union{Bool, Int} = true,
+            description = "",
             name)
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(dvs, ivs, ps)
@@ -127,7 +132,7 @@ struct PDESystem <: ModelingToolkit.AbstractMultivariateSystem
         end
 
         new(eqs, bcs, domain, ivs, dvs, ps, defaults, connector_type, systems, analytic,
-            analytic_func, name, metadata, gui_metadata)
+            analytic_func, name, description, metadata, gui_metadata)
     end
 end
 
diff --git a/test/components.jl b/test/components.jl
index 965578e0c5..ea63e3e758 100644
--- a/test/components.jl
+++ b/test/components.jl
@@ -41,7 +41,7 @@ end
 
 completed_rc_model = complete(rc_model)
 @test isequal(completed_rc_model.resistor.n.i, resistor.n.i)
-@test ModelingToolkit.n_extra_equations(capacitor) == 2
+@test ModelingToolkit.n_expanded_connection_equations(capacitor) == 2
 @test length(equations(structural_simplify(rc_model, allow_parameter = false))) == 2
 sys = structural_simplify(rc_model)
 @test_throws ModelingToolkit.RepeatedStructuralSimplificationError structural_simplify(sys)