addSummary: use opening and closing tags to select page summary. So summary doesn't have to be first thing in file.

a_pubfile.md

@@ -3,10 +3,12 @@ title: My Public File
 cuid: 26e4-a1
 ---
 
+<!--summary-start-->
+
 This is a public file with some nice text.
 
 It's easy to write in this file.
-<!--summary-above-->
+<!--summary-end-->
 I can write more things after the comment if I want.
 
 

html-manipulations/addSummary.js

@@ -1,6 +1,8 @@
 //looks for an html comment pattern, and, if found,
 //adds the text before it to the doc under the key `summary`.
-const reg = /^(?<summary>.+)?<!--summary-above-->/s
+const reg = /.*<!--summary-start-->(?<summary>.+)?<!--summary-end-->/s
+//use a custom element instead.
+// const reg = /<doc-summary>(?<summary>.+)?<\/doc-summary>/s
 export default (doc) => {
   const result = reg.exec(doc._body);
   if (result) {