udm_add_search_limit() adds search restrictions. 如果成功则返回 TRUE，失败则返回 FALSE。
agent - a link to Agent, received after call to udm_alloc_agent().
var - defines parameter, indicating limit.
val - defines the value of the current parameter.
Possible var values:
UDM_LIMIT_URL - defines document URL limitations to limit the search through subsection of the database. It supports SQL % and _ LIKE wildcards, where % matches any number of characters, even zero characters, and _ matches exactly one character. E.g. http://www.example.___/catalog may stand for http://www.example.com/catalog and http://www.example.net/catalog.
UDM_LIMIT_TAG - defines site TAG limitations. In indexer-conf you can assign specific TAGs to various sites and parts of a site. Tags in mnoGoSearch 3.1.x are lines, that may contain metasymbols % and _. Metasymbols allow searching among groups of tags. E.g. there are links with tags ABCD and ABCE, and search restriction is by ABC_ - the search will be made among both of the tags.
UDM_LIMIT_LANG - defines document language limitations.
UDM_LIMIT_CAT - defines document category limitations. Categories are similar to tag feature, but nested. So you can have one category inside another and so on. You have to use two characters for each level. Use a hex number going from 0-F or a 36 base number going from 0-Z. Therefore a top-level category like 'Auto' would be 01. If it has a subcategory like 'Ford', then it would be 01 (the parent category) and then 'Ford' which we will give 01. Put those together and you get 0101. If 'Auto' had another subcategory named 'VW', then it's id would be 01 because it belongs to the 'Ford' category and then 02 because it's the next category. So it's id would be 0102. If VW had a sub category called 'Engine' then it's id would start at 01 again and it would get the 'VW' id 02 and 'Auto' id of 01, making it 010201. If you want to search for sites under that category then you pass it cat=010201 in the URL.
UDM_LIMIT_DATE - defines limitation by date the document was modified.
Format of parameter value: a string with first character < or >, then with no space - date in unixtime format, for example:
If > character is used, then the search will be restricted to those documents having a modification date greater than entered, if <, then smaller.