# Topic proc (datum)

Source: https://ref.dm-lang.org/datum/proc/Topic

### Format
> `Topic(href,href_list[])`

### Args
- `href`: the hyperlink data (following ? in the URL).
- `href_list`: key/value list (from params2list(href)).


This procedure is called by the default `client.Topic()` proc when the href contains a parameter called "src" containing an object reference.

```dm /Topic/
mob/verb/test()
   usr << "Click <a href='?src=\ref[src];action=startgame'>here</a>!"
mob/Topic(href,href_list[])
   switch(href_list["action"])
      if("startgame")
         usr << "Starting game..."
```

The above example uses an embedded reference to the player's own mob to create a hyperlink to that mob's `Topic()` proc. You can easily add different actions, parameters, and so forth. Just remember that the parameter values are always stored as text, so you need to convert those to whatever data format you need using procedures such as `text2num()`, `locate()`, etc.

> [!danger]
> 
> Always validate the input in `Topic()` calls to make sure it's correct and the query you're recieving is legitimate.

### See also
- [Topic proc (client)](https://ref.dm-lang.org/client/proc/Topic.md)
- [ref text macro](https://ref.dm-lang.org/DM/text/macros/ref.md)