# Understanding Julia documentation syntax

**URL:** <https://discourse.julialang.org/t/understanding-julia-documentation-syntax/51484>\
**Category:** General Usage\
**Created:** [December 8, 2020, 11:21pm UTC](https://discourse.julialang.org/t/understanding-julia-documentation-syntax/51484 "2020-12-08T23:21:10Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Gregstrq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gregstrq/32/20620_2.png) [@Gregstrq](https://discourse.julialang.org/u/Gregstrq)\
**Post date:** [December 8, 2020, 11:21pm UTC](https://discourse.julialang.org/t/understanding-julia-documentation-syntax/51484/1 "2020-12-08T23:21:10Z")

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I’ve decided to familiarize myself with the documentaion system in Julia.  
For that, I am looking through the source Julia code as the source of inspiration.

However, I have encountered a puzzling syntax in one of the source files.  
Specifically, in base/abstractarrays.jl:

```julia
"""
    AbstractArray{T,N}
Supertype for `N`-dimensional arrays (or array-like types) with elements of type `T`.
[`Array`](@ref) and other types are subtypes of this. See the manual section on the
[`AbstractArray` interface](@ref man-interface-array).
"""
AbstractArray

```

Here, I see a docstring for abstract type `AbstractArray`. I expected that it should be followed by the definition of the type

```julia
abstract type AbstractArray{T,N} end

```

Instead, it is followed simply by `AbstractArray`. Could anyone explain this syntax to me, please?

---

<div class="post-metadata">

**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [December 8, 2020, 11:48pm UTC](https://discourse.julialang.org/t/understanding-julia-documentation-syntax/51484/2 "2020-12-08T23:48:35Z")

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My guess is that it is there solely for the purpose of documentation.  
The actual type is probably defined somewhere else.

---

<div class="post-metadata">

**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [December 9, 2020, 7:46am UTC](https://discourse.julialang.org/t/understanding-julia-documentation-syntax/51484/3 "2020-12-09T07:46:32Z")

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> [@Gregstrq](#):
>
> Could anyone explain this syntax to me, please?

Built-ins need a placeholder for the docstrings.

For user-defined types, you don’t need to worry about this.