docs: add docs for Equality, Flow, Stream and instream

Author: AayushSabharwal

src/systems/connectors.jl

@@ -94,6 +94,15 @@ is_domain_connector(s) = isconnector(s) && get_connector_type(s) === DomainConne
 
 get_systems(c::Connection) = c.systems
 
+"""
+    $(TYPEDSIGNATURES)
+
+`instream` is used when modeling stream connections. It is only allowed to be used on
+`Stream` variables.
+
+Refer to the [Connection semantics](@ref connect_semantics) section of the docs for more
+information.
+"""
 instream(a) = term(instream, unwrap(a), type = symtype(a))
 SymbolicUtils.promote_symtype(::typeof(instream), _) = Real
 

src/variables.jl

@@ -91,8 +91,50 @@ end
 
 ### Connect
 abstract type AbstractConnectType end
+"""
+    $(TYPEDEF)
+
+Flag which is meant to be passed to the `connect` metadata of a variable to affect how it
+behaves when the connector it is in is part of a `connect` equation. `Equality` is the
+default value and such variables when connected are made equal. For example, electric
+potential is equated at a junction.
+
+For more information, refer to the [Connection semantics](@ref connect_semantics) section
+of the docs.
+
+See also: [`Symbolics.connect`](@ref), [`@connector`](@ref), [`Flow`](@ref),
+[`Stream`](@ref).
+"""
 struct Equality <: AbstractConnectType end # Equality connection
+"""
+    $(TYPEDEF)
+
+Flag which is meant to be passed to the `connect` metadata of a variable to affect how it
+behaves when the connector it is in is part of a `connect` equation. `Flow` denotes that
+the sum of marked variable in all connectors in the connection set must sum to zero. For
+example, electric current sums to zero at a junction (assuming appropriate signs are used
+for current flowing in and out of the function).
+
+For more information, refer to the [Connection semantics](@ref connect_semantics) section
+of the docs.
+
+See also: [`Symbolics.connect`](@ref), [`@connector`](@ref), [`Equality`](@ref),
+[`Stream`](@ref).
+"""
 struct Flow <: AbstractConnectType end     # sum to 0
+"""
+    $(TYPEDEF)
+
+Flag which is meant to be passed to the `connect` metadata of a variable to affect how it
+behaves when the connector it is in is part of a `connect` equation. `Stream` denotes that
+the variable is part of a special stream connector.
+
+For more information, refer to the [Connection semantics](@ref connect_semantics) section
+of the docs.
+
+See also: [`Symbolics.connect`](@ref), [`@connector`](@ref), [`Equality`](@ref),
+[`Flow`](@ref).
+"""
 struct Stream <: AbstractConnectType end   # special stream connector
 
 """