Update phrasefunction.md

docs/features/phrasefunction.md

@@ -5,6 +5,7 @@ Feature group | Feature type | Data type | Available for node types
 [`Syntactic`](home.md#syntactic-features) | `node` | `string` | [`phrase`](phrasenodefeatures.md#readme)
 
 ## Feature description
+
 Phrase function (abbreviated)
 
 ## Feature values
@@ -21,7 +22,12 @@ V | Verbal function
 VC | Verbal Copula function
 
 ## Note
+
 See also the description in [MACULA Greek Treebank for the Nestle 1904 Greek New Testament.pdf](https://nbviewer.org/github/biblicalhumanities/greek-new-testament/blob/master/syntax-trees/nestle1904/doc/Nestle%201904%20Treebank%20Documentation.pdf) on page 5 and 6 (section 2.4 Syntactic Categories at Clause Level).
 
+## Source description
+
+Taken from (optional) XML attribute `Cat` for each element `node` representing a prhase.
+
 ---
 ###### [Click here for list of all features](home.md#readme)