I’m doing some testing with the Enterprise Search in SharePoint 2013 for a customer scenario and here are some observations…
Content Source as Crawled Property
The “Content Source” name is out of the box available as Managed Property on all content in the search index
This makes it possible to create Result Sources that aggregate content from different Content Sources similar to Search Scopes back in the old days.
Meta elements (HTML <meta> tags) as Crawled Properties
Information from meta elements in web pages is extracted into crawled properties
Consider the following example:
After crawling this website with SharePoint 2013 Search it will create (if new) or use (if existing) a Crawled Property and store the content from the meta element. The Crawled Property can then be mapped to Managed Properties to return, filter or sort query results.

Query string parameters as Crawled Properties
Query string parameters are not extracted into Crawled Properties
This was actually a request from the customer in order to be able to provide additional information regarding documents (on their website) into the search index. As I suspected it isn’t possible out of the box but you could definitely do it using Content Enrichment.
The “OriginalPath” is available as an input property for Content Enrichment and contains the exact url used for indexing the document:

With Content Enrichment it is pretty straightforward to look for predefined query string parameters and then map them to output properties.
$ssa = Get-SPEnterpriseSearchServiceApplication
$config = New-SPEnterpriseSearchContentEnrichmentConfiguration
$config.Endpoint = 'http://cews:818/ContentEnrichmentService2.svc'
$config.InputProperties = 'OriginalPath', 'ContentSource'
$config.OutputProperties = 'MyParam1', 'MyParam2'
$config.DebugMode = $false
$config.SendRawData = $false
Set-SPEnterpriseSearchContentEnrichmentConfiguration –SearchApplication $ssa –ContentEnrichmentConfiguration $config
More information on Content Enrichment from my SharePoint Saturday presentation: http://www.sharepointblogs.be/blogs/vandest/archive/2014/04/28/sharepoint-saturday-belgium-2014-content-enrichment-in-sharepoint-search.aspx
HTH