# Best way to extend a type doc string
**URL:** https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878
**Category:** General Usage
**Created:** [February 22, 2022, 3:58am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878 "2022-02-22T03:58:17Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@ablaom](https://discourse.julialang.org/u/ablaom)
#### Post date: [February 22, 2022, 3:58am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878/1 "2022-02-22T03:58:17Z")
Pkg A defines some type `Foo`, and this includes the declaration of a document string.
Pkg B extends the functionality of `Foo` objects and wants to _extend_, not replace, the type’s docstring.
What’s a clean way to do this?
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [February 22, 2022, 4:29am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878/2 "2022-02-22T04:29:48Z")
“it just works”
```julia
julia> module A
"""
docstring in A
"""
struct aa end
end
Main.A
help?> Main.A.aa
docstring in A
julia> module B
using Main.A
"""
docstring in B
"""
Main.A.aa
end
Main.B
help?> Main.A.aa
docstring in A
───────────────────────────────────────────────────────────────────────────────────────────────────────
docstring in B
```
---
### Author:  [@ablaom](https://discourse.julialang.org/u/ablaom)
#### Post date: [February 22, 2022, 5:49am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878/3 "2022-02-22T05:49:08Z")
Great. That answers the question that I posed!
But what if I want to do the extension in the same module. That does not “just work”, right?
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [February 22, 2022, 5:50am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878/4 "2022-02-22T05:50:25Z")
It should just work, much like you can have separate docstring for each method and they all show up
---
### Author:  [@ablaom](https://discourse.julialang.org/u/ablaom)
#### Post date: [February 22, 2022, 6:01am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878/5 "2022-02-22T06:01:00Z")
It doesn’t seem to work:
```julia
"""
line 1
"""
struct Goo end
julia> @doc Goo
line 1
# now add post facto:
@doc """line2""" Goo
julia> @doc Goo
line 2
```
“line 1” has been replaced.
What am I missing?
---
### Author:  [@Ralph\_Smith](https://discourse.julialang.org/u/Ralph_Smith)
#### Post date: [February 25, 2022, 4:43am UTC](https://discourse.julialang.org/t/best-way-to-extend-a-type-doc-string/76878/6 "2022-02-25T04:43:15Z")
1. a docstring is registered in the module where it is defined.
2. only one docstring in a module is associated with a (function/type, signature) pair
a. defining another one replaces the incumbent.
3. a docstring for a bare type has a null signature (i.e., `Union{}`)
a. constructors can add new docstrings.