C# provides a mechanism for programmers to document their code using a special comment syntax that contains XML text. In source code files, comments having a certain form can be used to direct a tool to produce XML from those comments and the source code elements, which they precede. Comments using such syntax are called ***documentation comments***. They must immediately precede a user-defined type (such as a class, delegate, or interface) or a member (such as a field, event, property, or method). The XML generation tool is called the ***documentation generator***. (This generator could be, but need not be, the C# compiler itself.) The output produced by the documentation generator is called the ***documentation file***. A documentation file is used as input to a ***documentation viewer***; a tool intended to produce some sort of visual display of type information and its associated documentation.
This specification suggests a set of tags to be used in documentation comments, but use of these tags is not required, and other tags may be used if desired, as long the rules of well-formed XML are followed.
## Introduction
Comments having a special form can be used to direct a tool to produce XML from those comments and the source code elements, which they precede. Such comments are single-line comments that start with three slashes (`///`), or delimited comments that start with a slash and two stars (`/**`). They must immediately precede a user-defined type (such as a class, delegate, or interface) or a member (such as a field, event, property, or method) that they annotate. Attribute sections ([Attribute specification](attributes.md#attribute-specification)) are considered part of declarations, so documentation comments must precede attributes applied to a type or member.
In a *single_line_doc_comment*, if there is a *whitespace* character following the `///` characters on each of the *single_line_doc_comment*s adjacent to the current *single_line_doc_comment*, then that *whitespace* character is not included in the XML output.
In a delimited-doc-comment, if the first non-whitespace character on the second line is an asterisk and the same pattern of optional whitespace characters and an asterisk character is repeated at the beginning of each of the line within the delimited-doc-comment, then the characters of the repeated pattern are not included in the XML output. The pattern may include whitespace characters after, as well as before, the asterisk character.
__Example:__
```csharp
/// <summary>Class <c>Point</c> models a point in a two-dimensional
/// plane.</summary>
///
public class Point
{
/// <summary>method <c>draw</c> renders the point.</summary>
The text within documentation comments must be well formed according to the rules of XML (https://www.w3.org/TR/REC-xml). If the XML is ill formed, a warning is generated and the documentation file will contain a comment saying that an error was encountered.
Although developers are free to create their own set of tags, a recommended set is defined in [Recommended tags](documentation-comments.md#recommended-tags). Some of the recommended tags have special meanings:
* The `<param>` tag is used to describe parameters. If such a tag is used, the documentation generator must verify that the specified parameter exists and that all parameters are described in documentation comments. If such verification fails, the documentation generator issues a warning.
* The `cref` attribute can be attached to any tag to provide a reference to a code element. The documentation generator must verify that this code element exists. If the verification fails, the documentation generator issues a warning. When looking for a name described in a `cref` attribute, the documentation generator must respect namespace visibility according to `using` statements appearing within the source code. For code elements that are generic, the normal generic syntax (that is, "`List<T>`") cannot be used because it produces invalid XML. Braces can be used instead of brackets (that is, "`List{T}`"), or the XML escape syntax can be used (that is, "`List<T>`").
* The `<summary>` tag is intended to be used by a documentation viewer to display additional information about a type or member.
* The `<include>` tag includes information from an external XML file.
Note carefully that the documentation file does not provide full information about the type and members (for example, it does not contain any type information). To get such information about a type or member, the documentation file must be used in conjunction with reflection on the actual type or member.
## Recommended tags
The documentation generator must accept and process any tag that is valid according to the rules of XML. The following tags provide commonly used functionality in user documentation. (Of course, other tags are possible.)
| `<returns>` | [`<returns>`](documentation-comments.md#returns) | Describe the return value of a method |
| `<see>` | [`<see>`](documentation-comments.md#see) | Specify a link |
| `<seealso>` | [`<seealso>`](documentation-comments.md#seealso) | Generate a See Also entry |
| `<summary>` | [`<summary>`](documentation-comments.md#summary) | Describe a type or a member of a type |
| `<value>` | [`<value>`](documentation-comments.md#value) | Describe a property |
| `<typeparam>` | | Describe a generic type parameter |
| `<typeparamref>` | | Identify that a word is a type parameter name |
### `<c>`
This tag provides a mechanism to indicate that a fragment of text within a description should be set in a special font such as that used for a block of code. For lines of actual code, use `<code>` ([`<code>`](documentation-comments.md#code)).
__Syntax:__
```xml
<c>text</c>
```
__Example:__
```csharp
/// <summary>Class <c>Point</c> models a point in a two-dimensional
/// plane.</summary>
public class Point
{
// ...
}
```
### `<code>`
This tag is used to set one or more lines of source code or program output in some special font. For small code fragments in narrative, use `<c>` ([`<c>`](documentation-comments.md#c)).
__Syntax:__
```xml
<code>source code or program output</code>
```
__Example:__
```csharp
/// <summary>This method changes the point's location by
/// the given x- and y-offsets.
/// <example>For example:
/// <code>
/// Point p = new Point(3,5);
/// p.Translate(-1,3);
/// </code>
/// results in <c>p</c>'s having the value (2,8).
/// </example>
/// </summary>
public void Translate(int xor, int yor) {
X += xor;
Y += yor;
}
```
### `<example>`
This tag allows example code within a comment, to specify how a method or other library member may be used. Ordinarily, this would also involve use of the tag `<code>` ([`<code>`](documentation-comments.md#code)) as well.
__Syntax:__
```xml
<example>description</example>
```
__Example:__
See `<code>` ([`<code>`](documentation-comments.md#code)) for an example.
### `<exception>`
This tag provides a way to document the exceptions a method can throw.
__Syntax:__
```xml
<exceptioncref="member">description</exception>
```
where
*`member` is the name of a member. The documentation generator checks that the given member exists and translates `member` to the canonical element name in the documentation file.
*`description` is a description of the circumstances in which the exception is thrown.
This tag allows including information from an XML document that is external to the source code file. The external file must be a well-formed XML document, and an XPath expression is applied to that document to specify what XML from that document to include. The `<include>` tag is then replaced with the selected XML from the external document.
and the external file "docs.xml" had the following contents:
```xml
<?xml version="1.0"?>
<extradoc>
<classname="IntList">
<summary>
Contains a list of integers.
</summary>
</class>
<classname="StringList">
<summary>
Contains a list of integers.
</summary>
</class>
</extradoc>
```
then the same documentation is output as if the source code contained:
```csharp
/// <summary>
/// Contains a list of integers.
/// </summary>
public class IntList { ... }
```
### `<list>`
This tag is used to create a list or table of items. It may contain a `<listheader>` block to define the heading row of either a table or definition list. (When defining a table, only an entry for `term` in the heading need be supplied.)
Each item in the list is specified with an `<item>` block. When creating a definition list, both `term` and `description` must be specified. However, for a table, bulleted list, or numbered list, only `description` need be specified.
__Syntax:__
```xml
<listtype="bullet"|"number"|"table">
<listheader>
<term>term</term>
<description>*description*</description>
</listheader>
<item>
<term>term</term>
<description>*description*</description>
</item>
...
<item>
<term>term</term>
<description>description</description>
</item>
</list>
```
where
*`term` is the term to define, whose definition is in `description`.
*`description` is either an item in a bullet or numbered list, or the definition of a `term`.
__Example:__
```csharp
public class MyClass
{
/// <summary>Here is an example of a bulleted list:
This tag is for use inside other tags, such as `<summary>` ([`<remarks>`](documentation-comments.md#remarks)) or `<returns>` ([`<returns>`](documentation-comments.md#returns)), and permits structure to be added to text.
/// <paramname="xor">the new Point's x-coordinate.</param>
/// <paramname="yor">the new Point's y-coordinate.</param>
public Point(int xor, int yor) {
X = xor;
Y = yor;
}
```
### `<permission>`
This tag allows the security accessibility of a member to be documented.
__Syntax:__
```xml
<permissioncref="member">description</permission>
```
where
*`member` is the name of a member. The documentation generator checks that the given code element exists and translates *member* to the canonical element name in the documentation file.
*`description` is a description of the access to the member.
__Example:__
```csharp
/// <permissioncref="System.Security.PermissionSet">Everyone can
This tag is used to specify extra information about a type. (Use `<summary>` ([`<summary>`](documentation-comments.md#summary)) to describe the type itself and the members of a type.)
This tag is used to describe the return value of a method.
__Syntax:__
```xml
<returns>description</returns>
```
where `description` is a description of the return value.
__Example:__
```csharp
/// <summary>Report a point's location as a string.</summary>
/// <returns>A string representing a point's location, in the form (x,y),
/// without any leading, trailing, or embedded whitespace.</returns>
public override string ToString() {
return "(" + X + "," + Y + ")";
}
```
### `<see>`
This tag allows a link to be specified within text. Use `<seealso>` ([`<seealso>`](documentation-comments.md#seealso)) to indicate text that is to appear in a See Also section.
__Syntax:__
```xml
<seecref="member"/>
```
where `member` is the name of a member. The documentation generator checks that the given code element exists and changes *member* to the element name in the generated documentation file.
__Example:__
```csharp
/// <summary>This method changes the point's location to
/// the given coordinates.</summary>
/// <seecref="Translate"/>
public void Move(int xor, int yor) {
X = xor;
Y = yor;
}
/// <summary>This method changes the point's location by
/// the given x- and y-offsets.
/// </summary>
/// <seecref="Move"/>
public void Translate(int xor, int yor) {
X += xor;
Y += yor;
}
```
### `<seealso>`
This tag allows an entry to be generated for the See Also section. Use `<see>` ([`<see>`](documentation-comments.md#see)) to specify a link from within text.
__Syntax:__
```xml
<seealsocref="member"/>
```
where `member` is the name of a member. The documentation generator checks that the given code element exists and changes *member* to the element name in the generated documentation file.
__Example:__
```csharp
/// <summary>This method determines whether two Points have the same
This tag can be used to describe a type or a member of a type. Use `<remarks>` ([`<remarks>`](documentation-comments.md#remarks)) to describe the type itself.
where `description` is a summary of the type or member.
__Example:__
```csharp
/// <summary>This constructor initializes the new Point to (0,0).</summary>
public Point() : this(0,0) {
}
```
### `<value>`
This tag allows a property to be described.
__Syntax:__
```xml
<value>property description</value>
```
where `property description` is a description for the property.
__Example:__
```csharp
/// <value>Property <c>X</c> represents the point's x-coordinate.</value>
public int X
{
get { return x; }
set { x = value; }
}
```
### `<typeparam>`
This tag is used to describe a generic type parameter for a class, struct, interface, delegate, or method.
__Syntax:__
```xml
<typeparamname="name">description</typeparam>
```
where `name` is the name of the type parameter, and `description` is its description.
__Example:__
```csharp
/// <summary>A generic list class.</summary>
/// <typeparamname="T">The type stored by the list.</typeparam>
public class MyList<T> {
...
}
```
### `<typeparamref>`
This tag is used to indicate that a word is a type parameter. The documentation file can be processed to format this type parameter in some distinct way.
__Syntax:__
```xml
<typeparamrefname="name"/>
```
where `name` is the name of the type parameter.
__Example:__
```csharp
/// <summary>This method fetches data and returns a list of <typeparamrefname="T"/>.</summary>
/// <paramname="query">query to execute</param>
public List<T> FetchData<T>(string query) {
...
}
```
## Processing the documentation file
The documentation generator generates an ID string for each element in the source code that is tagged with a documentation comment. This ID string uniquely identifies a source element. A documentation viewer can use an ID string to identify the corresponding metadata/reflection item to which the documentation applies.
The documentation file is not a hierarchical representation of the source code; rather, it is a flat list with a generated ID string for each element.
### ID string format
The documentation generator observes the following rules when it generates the ID strings:
* No white space is placed in the string.
* The first part of the string identifies the kind of member being documented, via a single character followed by a colon. The following kinds of members are defined:
| M | Method (including constructors, destructors, and operators) |
| N | Namespace |
| P | Property (including indexers) |
| T | Type (such as class, delegate, enum, interface, and struct) |
| ! | Error string; the rest of the string provides information about the error. For example, the documentation generator generates error information for links that cannot be resolved. |
* The second part of the string is the fully qualified name of the element, starting at the root of the namespace. The name of the element, its enclosing type(s), and namespace are separated by periods. If the name of the item itself has periods, they are replaced by `#(U+0023)` characters. (It is assumed that no element has this character in its name.)
* For methods and properties with arguments, the argument list follows, enclosed in parentheses. For those without arguments, the parentheses are omitted. The arguments are separated by commas. The encoding of each argument is the same as a CLI signature, as follows:
* Arguments are represented by their documentation name, which is based on their fully qualified name, modified as follows:
* Arguments having the `out` or `ref` modifier have an `@` following their type name. Arguments passed by value or via `params` have no special notation.
* Arguments that are arrays are represented as `[lowerbound:size, ... , lowerbound:size]` where the number of commas is the rank less one, and the lower bounds and size of each dimension, if known, are represented in decimal. If a lower bound or size is not specified, it is omitted. If the lower bound and size for a particular dimension are omitted, the `:` is omitted as well. Jagged arrays are represented by one `[]` per level.
* Arguments that have pointer types other than void are represented using a `*` following the type name. A void pointer is represented using a type name of `System.Void`.
* Arguments that refer to generic type parameters defined on types are encoded using the `` ` `` (backtick) character followed by the zero-based index of the type parameter.
* Arguments that use generic type parameters defined in methods use a double-backtick ``` `` ``` instead of the `` ` `` used for types.
* Arguments that refer to constructed generic types are encoded using the generic type, followed by `{`, followed by a comma-separated list of type arguments, followed by `}`.
The following examples each show a fragment of C# code, along with the ID string produced from each source element capable of having a documentation comment:
* Types are represented using their fully qualified name, augmented with generic information:
```csharp
enum Color { Red, Blue, Green }
namespace Acme
{
interface IProcess {...}
struct ValueType {...}
class Widget: IProcess
{
public class NestedClass {...}
public interface IMenuItem {...}
public delegate void Del(int i);
public enum Direction { North, South, East, West }
}
class MyList<T>
{
class Helper<U,V> {...}
}
}
"T:Color"
"T:Acme.IProcess"
"T:Acme.ValueType"
"T:Acme.Widget"
"T:Acme.Widget.NestedClass"
"T:Acme.Widget.IMenuItem"
"T:Acme.Widget.Del"
"T:Acme.Widget.Direction"
"T:Acme.MyList`1"
"T:Acme.MyList`1.Helper`2"
```
* Fields are represented by their fully qualified name:
```csharp
namespace Acme
{
struct ValueType
{
private int total;
}
class Widget: IProcess
{
public class NestedClass
{
private int value;
}
private string message;
private static Color defaultColor;
private const double PI = 3.14159;
protected readonly double monthlyAverage;
private long[] array1;
private Widget[,] array2;
private unsafe int *pCount;
private unsafe float **ppValues;
}
}
"F:Acme.ValueType.total"
"F:Acme.Widget.NestedClass.value"
"F:Acme.Widget.message"
"F:Acme.Widget.defaultColor"
"F:Acme.Widget.PI"
"F:Acme.Widget.monthlyAverage"
"F:Acme.Widget.array1"
"F:Acme.Widget.array2"
"F:Acme.Widget.pCount"
"F:Acme.Widget.ppValues"
```
* Constructors.
```csharp
namespace Acme
{
class Widget: IProcess
{
static Widget() {...}
public Widget() {...}
public Widget(string s) {...}
}
}
"M:Acme.Widget.#cctor"
"M:Acme.Widget.#ctor"
"M:Acme.Widget.#ctor(System.String)"
```
* Destructors.
```csharp
namespace Acme
{
class Widget: IProcess
{
~Widget() {...}
}
}
"M:Acme.Widget.Finalize"
```
* Methods.
```csharp
namespace Acme
{
struct ValueType
{
public void M(int i) {...}
}
class Widget: IProcess
{
public class NestedClass
{
public void M(int i) {...}
}
public static void M0() {...}
public void M1(char c, out float f, ref ValueType v) {...}
public void M2(short[] x1, int[,] x2, long[][] x3) {...}
public void M3(long[][] x3, Widget[][,,] x4) {...}
public unsafe void M4(char *pc, Color **pf) {...}
public unsafe void M5(void *pv, double *[][,] pd) {...}
public void M6(int i, params object[] args) {...}
}
class MyList<T>
{
public void Test(T t) { }
}
class UseList
{
public void Process(MyList<int> list) { }
public MyList<T> GetValues<T>(T inputValue) { return null; }
public int this[string s, int i] { get {...} set {...} }
}
}
"P:Acme.Widget.Width"
"P:Acme.Widget.Item(System.Int32)"
"P:Acme.Widget.Item(System.String,System.Int32)"
```
* Events.
```csharp
namespace Acme
{
class Widget: IProcess
{
public event Del AnEvent;
}
}
"E:Acme.Widget.AnEvent"
```
* Unary operators.
```csharp
namespace Acme
{
class Widget: IProcess
{
public static Widget operator+(Widget x) {...}
}
}
"M:Acme.Widget.op_UnaryPlus(Acme.Widget)"
```
The complete set of unary operator function names used is as follows: `op_UnaryPlus`, `op_UnaryNegation`, `op_LogicalNot`, `op_OnesComplement`, `op_Increment`, `op_Decrement`, `op_True`, and `op_False`.
* Binary operators.
```csharp
namespace Acme
{
class Widget: IProcess
{
public static Widget operator+(Widget x1, Widget x2) {...}
The complete set of binary operator function names used is as follows: `op_Addition`, `op_Subtraction`, `op_Multiply`, `op_Division`, `op_Modulus`, `op_BitwiseAnd`, `op_BitwiseOr`, `op_ExclusiveOr`, `op_LeftShift`, `op_RightShift`, `op_Equality`, `op_Inequality`, `op_LessThan`, `op_LessThanOrEqual`, `op_GreaterThan`, and `op_GreaterThanOrEqual`.
* Conversion operators have a trailing "`~`" followed by the return type.
```csharp
namespace Acme
{
class Widget: IProcess
{
public static explicit operator int(Widget x) {...}
public static implicit operator long(Widget x) {...}
