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Merge pull request #50250 from johanngan/regexptree-doc-tweaks

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Clean up regexp tree dictionary documentation
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@ -2234,7 +2234,7 @@ Result:
## Regular Expression Tree Dictionary {#regexp-tree-dictionary} ## Regular Expression Tree Dictionary {#regexp-tree-dictionary}
Regular expression tree dictionaries are a special type of dictionary which represent the mapping from key to attributes using a tree of regular expressions. There are some use cases, e.g. parsing of (user agent)[https://en.wikipedia.org/wiki/User_agent] strings, which can be expressed elegantly with regexp tree dictionaries. Regular expression tree dictionaries are a special type of dictionary which represent the mapping from key to attributes using a tree of regular expressions. There are some use cases, e.g. parsing of [user agent](https://en.wikipedia.org/wiki/User_agent) strings, which can be expressed elegantly with regexp tree dictionaries.
### Use Regular Expression Tree Dictionary in ClickHouse Open-Source ### Use Regular Expression Tree Dictionary in ClickHouse Open-Source
@ -2280,7 +2280,7 @@ This config consists of a list of regular expression tree nodes. Each node has t
- The value of an attribute may contain **back references**, referring to capture groups of the matched regular expression. In the example, the value of attribute `version` in the first node consists of a back-reference `\1` to capture group `(\d+[\.\d]*)` in the regular expression. Back-reference numbers range from 1 to 9 and are written as `$1` or `\1` (for number 1). The back reference is replaced by the matched capture group during query execution. - The value of an attribute may contain **back references**, referring to capture groups of the matched regular expression. In the example, the value of attribute `version` in the first node consists of a back-reference `\1` to capture group `(\d+[\.\d]*)` in the regular expression. Back-reference numbers range from 1 to 9 and are written as `$1` or `\1` (for number 1). The back reference is replaced by the matched capture group during query execution.
- **child nodes**: a list of children of a regexp tree node, each of which has its own attributes and (potentially) children nodes. String matching proceeds in a depth-first fashion. If a string matches a regexp node, the dictionary checks if it also matches the nodes' child nodes. If that is the case, the attributes of the deepest matching node are assigned. Attributes of a child node overwrite equally named attributes of parent nodes. The name of child nodes in YAML files can be arbitrary, e.g. `versions` in above example. - **child nodes**: a list of children of a regexp tree node, each of which has its own attributes and (potentially) children nodes. String matching proceeds in a depth-first fashion. If a string matches a regexp node, the dictionary checks if it also matches the nodes' child nodes. If that is the case, the attributes of the deepest matching node are assigned. Attributes of a child node overwrite equally named attributes of parent nodes. The name of child nodes in YAML files can be arbitrary, e.g. `versions` in above example.
Regexp tree dictionaries only allow access using functions `dictGet`, `dictGetOrDefault` and `dictGetOrNull`. Regexp tree dictionaries only allow access using the functions `dictGet` and `dictGetOrDefault`.
Example: Example: