Merge commit 'b9bd35d72e14932fb6588ff62b90cddef0a060fc' as 'docs'

docs/content/en/functions/isset.md

@@ -0,0 +1,32 @@
+---
+title: isset
+linktitle: isset
+description: Returns true if the parameter is set.
+godocref:
+date: 2017-02-01
+publishdate: 2017-02-01
+lastmod: 2017-02-01
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: []
+signature: ["isset COLLECTION INDEX", "isset COLLECTION KEY"]
+workson: []
+hugoversion:
+relatedfuncs: []
+deprecated: false
+aliases: []
+---
+
+Takes either a slice, array, or channel and an index or a map and a key as input.
+
+```
+{{ if isset .Params "project_url" }} {{ index .Params "project_url" }}{{ end }}
+```
+
+{{% warning %}}
+All site-level configuration keys are stored as lower case. Therefore, a `myParam` key-value set in your [site configuration file](/getting-started/configuration/) needs to be accessed with `{{if isset .Site.Params "myparam"}}` and *not* with `{{if isset .Site.Params "myParam"}}`. Note that you can still access the same config key with `.Site.Params.myParam` *or* `.Site.Params.myparam`, for example, when using [`with`](/functions/with).
+This restriction also applies when accessing page-level front matter keys from within [shortcodes](/content-management/shortcodes/).
+{{% /warning %}}
+