At the most basic level a rule is a regular expression to match a given input (either a URL or the content type of the URL) and one or more flags to control behaviour.
When a website is crawled, for each detected URL all enabled rules are ran. If the expression for a rule is a match for the URL or content type, then behaviour actions are processed.
If a rule fails to execute, for example due to an invalid regular expression, the rule will be automatically disabled.
| Expression | Description |
|---|---|
| Compare | Allows you to choose what the pattern will be matched to, for example just the query string of a URL, or the content type |
| Expression | Specifies an expression that will be matched against the input. You can use regular expressions for more advanced control |
If your expression includes any of the ^, [, ., $, {, *, (, \, +, ), |, ?, <, > characters and you want them to processed as plain text, you need to "escape" the character by preceding it with a backslash. For example, if your expression was application/epub+zip this would need to be written as application/epub\+zip otherwise the + character would have a special meaning and no matches would be made. Similarly, if the expression was example.com, this should be written as example\.com, as . means "any character" which could lead to unexpected matches.
This table outlines the different compare options available. The example match is based on the following sample address
http://www.example.com/folder/products?sort=name&order=asc
| Option | Description | Example |
|---|---|---|
| Authority | The URL domain | www.example.com |
| Authority, Path, and Query String | The domain, path and query string of the URL | www.example.com/folder/products?sort=name&order=asc |
| Content Type | The detected content type of the URL | text/html |
| Entire URL | The complete URL | http://www.example.com/folder/products?sort=name&order=asc |
| Path | The path of the URL, including file names if applicable | folder/products |
| Path and Query String | The path and query string of the URL | folder/products?sort=name&order=asc |
| Query String | The query string of the URL | sort=name&order=asc |
| Operand | Description |
|---|---|
| Matches | Specifies the rule will be processed if the given input matches the rule expression |
| Does Not Match | Specifies the rule will be processed if the given input does not match the rule expression |
| Option | Description |
|---|---|
| Enable this rule | Specifies if the rule is enabled or not. Disabled rules will be ignored |
| Exclude | Specifies that the URL should not be downloaded |
| Exclude, but scan for additional content | Specifies that although the URL is excluded and will not be permanently saved, its contents should still be scanned (applies to HTML documents only). This means that although a permanent copy of the URL is not downloaded, a temporary copy is still made in order to scan for additional URLs to crawl. |
| Download | Specifies that the URL should be downloaded. This allows you to have a wider rule to exclude content, and then a narrower rule to include specific content. |
| Download, but do not scan for additional content | Specifies that although the URL is downloaded, its contents should not be scanned. This means that while a permanent copy of the URL is created, it will not be scanned for additional URLs to crawl. This option applies to HTML documents only |
| Stop processing more rules | By default all rules are processed sequentially. You can use this flag to control this process; if set and the rule is matched, no further rules will be processed |
| Download Priority | Allows the download priority for URLs matching the rule to be changed. High priority will mean the URL will be downloaded immediately, while Low means the URL will be downloaded when all other URLs have been processed1. |
1 The Download Priority options is only supported for rules that match against a URL, it is ignored for rules matching against content types.