Advanced Programmable Search Engine features

To manage your advanced search controls, click Overview and scroll down to Search features. Click on "All search features settings". Then scroll down to Advanced settings. 

Search Control	Details	Supported Values
Results sorting
Enable results sorting	Sort results using either date or other structured content. This configuration should match the configuration set under Control Panel > Overview > Search features > Advanced settings > Results Sorting. Please scroll down to Results sorting for details.	Enable, Disable
Web Search settings
Results browsing history	Enables the user of the browser Back button to view previous search results pages.	Enable, Disable
Structured data in results	Shows structured data in results	Enable, Disabled
'No results' message	Specifies the default text to display when no results match the query.	Text
Link target	Sets the link target for links embedded in search results.	blank, _self, top_frame, server
Query parameter name	A string that specifies the query parameter name in the result URL.	Any string to identify the query in search. Should match the string (if any) used in Google Analytics
Web Search restricts
Language restrict	Restricts search results to documents written in a particular language.	Supported languages
Results per page	Number of results to return per user query.	Integer between 1 and 20
Site search restriction	Restrict results to pages from a specific site.	URL of a site
Filter similar results	Automatic filtering of search results.	Enable, Disable
Image Search settings
Many restricts available for Web Search are also available in Image Search settings. See Web Search restricts for available options. Note: You need to first enable "Image Search" from Search features under Overview to have this Image Search settings displayed.
Default to Image Search	Default search results to Image Search results	Enable, Disable

Results sorting

When you enable search results sorting, Programmable Search Engine automatically lets you sort results by date and by relevance. If you use PageMaps, meta tags, or rich snippets markup to create structured data on your pages, you can enable also sorting by additional properties used in your markup.

For example, if your content is marked up with Reviews rich snippets, you could enable sorting by rating (number of stars) or other numerical key. If your content includes a PageMap identifying a publication, you can sort results by Publication Date.

Enable search Results sorting:

1. On the Control Panel, click Overview and scroll down to Search features. Click on "All search features settings". Then scroll down to Advanced settings. 
2. In Results sorting section below, select toggle "Enable results sorting" to enable/disable results sorting.
3. (Optional) To add a custom sorting key:
   1. Click Add.
   2. In the Key box, type the key name you want to appear on the search results page. Users will click this name to sort results. 
   3. In the Key Label box, type the property you want to sort by. This should exactly match the DataObject name (PageMaps) or property (rich snippets) used for your content. (To see the available keys, use the rich snippets testing tool.)
   4. Click Save.

By default Programmable Search Engine enables sorting of results by "Relevancy". From "Default Web Search sorting"/ "Default image search sorting" set the default Web Search results sorting style from the sorting results drop down list.

Note : You can even add your own custom Label name and Key, or edit the existing  Label names (even including the default "Relevance" and "Date" Label names) to your own custom names.