Merge commit '9b0050e9aabe4be65c78ccf292a348f309d50ccd' as 'docs'

```
git subtree add --prefix=docs/ https://github.com/gohugoio/hugoDocs.git master --squash
```

Closes #11925

docs/content/en/functions/strings/Substr.md

@@ -0,0 +1,38 @@
+---
+title: strings.Substr
+description: Extracts parts of a string from a specified character's position and returns the specified number of characters.
+categories: []
+keywords: []
+action:
+  aliases: [substr]
+  related: []
+  returnType: string
+  signatures: ['strings.Substr STRING START [LENGTH]']
+aliases: [/functions/substr]
+---
+
+It normally takes two argument: `start` and `length`. It can also take one argument: `start`, i.e. `length` is omitted, in which case the substring starting from start until the end of the string will be returned.
+
+To extract characters from the end of the string, use a negative start number.
+
+If `length` is given and is negative, that number of characters will be omitted from the end of string.
+
+```go-html-template
+{{ substr "abcdef" 0 }} → abcdef
+{{ substr "abcdef" 1 }} → bcdef
+
+{{ substr "abcdef" 0 1 }} → a
+{{ substr "abcdef" 1 1 }} → b
+
+{{ substr "abcdef" 0 -1 }} → abcde
+{{ substr "abcdef" 1 -1 }} → bcde
+
+{{ substr "abcdef" -1 }} → f
+{{ substr "abcdef" -2 }} → ef
+
+{{ substr "abcdef" -1 1 }} → f
+{{ substr "abcdef" -2 1 }} → e
+
+{{ substr "abcdef" -3 -1 }} → de
+{{ substr "abcdef" -3 -2 }} → d
+```