refactor: mark VariableType, MTKVariableTypeCtx as public

Author: AayushSabharwal

docs/src/API/variables.md

@@ -263,6 +263,15 @@ hasunit
 getunit
 ```
 
+## Variable type
+
+This metadata is used by the [`System`](@ref) constructor for automatically identifying the different types of variables in a system.
+
+```@docs
+ModelingToolkit.VariableType
+ModelingToolkit.MTKVariableTypeCtx
+```
+
 ## Miscellaneous metadata
 
 User-defined metadata can be added using the `misc` metadata. This can be queried

src/ModelingToolkit.jl

@@ -339,6 +339,7 @@ export DynamicOptSolution
 @public AbstractSystem, CheckAll, CheckNone, CheckComponents, CheckUnits
 @public t, D, t_nounits, D_nounits, t_unitful, D_unitful
 @public SymbolicContinuousCallback, SymbolicDiscreteCallback
+@public VariableType, MTKVariableTypeCtx
 
 for prop in [SYS_PROPS; [:continuous_events, :discrete_events]]
     getter = Symbol(:get_, prop)

src/parameters.jl

@@ -1,5 +1,18 @@
 import SymbolicUtils: symtype, term, hasmetadata, issym
+
+"""
+    @enum VariableType
+
+The type of the declared variable, used for automatic identification of
+variables/parameters/brownians/etc. by the `System` constructor.
+"""
 @enum VariableType VARIABLE PARAMETER BROWNIAN
+
+"""
+    $TYPEDEF
+
+The symbolic metadata key for storing the `VariableType`.
+"""
 struct MTKVariableTypeCtx end
 
 getvariabletype(x, def = VARIABLE) = getmetadata(unwrap(x), MTKVariableTypeCtx, def)