>> I had thought about the `\[[!tag type1=value1 type2=value2]]` syntax myself, but ultimately decided against it for a number of reasons, most importantly the fact that (1) it's harder to type, (2) it's harder to spot errors in the tag types (so for example if one misspelled `categoria` as `categorica`, he might not notice it as quickly as seeing the un-parsed `\[[!categorica ]]` directive in the output html) and (3) it encourages collapsing possibly unrelated metadata together (for example, I would never consider putting the categoria information together with the rubrica one; of course with your syntax it's perfectly possible to keep them separate as well).
->> Point (2) may be considered a downside as well as an upside, depending on perspective, of course. And it would be possible to have a set of predefined tag types to match against, like in my tagtype directive approach but with your syntax. Point (3) is of course entirely in the hands of the user, but that's exactly what syntax should be about. There is nothing functionally wrong with e.g. `\[[!meta tag=sometag author=someauthor title=sometitle rubrica=somecolumn]]`, but I honestly find it horrible.
+>> Point (2) may be considered a downside as well as an upside, depending on perspective, of course. And it would be possible to have a set of predefined tag types to match against, like in my tagtype directive approach but with your syntax.
+
+>>> You seem to have answered your own objections already. -- K.A.
+
+>>Point (3) is of course entirely in the hands of the user, but that's exactly what syntax should be about. There is nothing functionally wrong with e.g. `\[[!meta tag=sometag author=someauthor title=sometitle rubrica=somecolumn]]`, but I honestly find it horrible.
+
+>>> So, really, point 3 comes down to differing aesthetics. -- K.A.
>> A solution could be to allow both syntaxes, getting to have for example `\[[!sometagtype "blah"]]` as a shortcut for `\[[!tag sometagtype="blah"]]` (or, in the more general case, `\[[!somefieldname "blah"]]` as a shortcut for `\[[!meta fieldname="blah"]]`).
>> I would like to point out however that there are some functional differences between categorization metadata vs other metadata that might suggest to keep fields and (my extended) tags separate. For examples, in feeds you'd want all categorization metadata to fall in one place, with some appropriate manipulation (which I still have to implement, by the way), while things like author or title would go to the corresponding feed item properties. Although it all would be possible with appropriate report or template juggling, having such default metadata handled natively looks like a bonus to me.
+
+>>> Whereas I prefer being able to control such things with templates, because it gives more flexibility AND control. - K.A.
+
+>>>> Flexibility and control is good for tuning and power-usage, but sensible defaults are a must for a platform to be usable out of the box without much intervention. Moreover, there's a possible problem with what kind of data must be passed over to templates.
+
+Aside from the name of the plugin (and thus of the main directive), which could be `tag`, `meta`, `field` or whatever (maybe extending `meta` would be the most sensible choice), the features we want are
+
+ 1. allow multiple values per type/attribute/field/whatever (fields currently only allows one)
+ 2. allow both hidden and visible references (à la tag vs taglink)
+ 3. allow each type/attribute/field to be exposed under multiple queries (e.g. tags and categories; this is mostly important for backwards compatibility, not sure if it might have other uses too)
+ 4. allow arbitrary types/attributes/fields/whatever (even 'undefined' ones)
+
+Each type/attribute/field/whatever (predefined, user-defined, arbitrary) would thus have the following parameters:
+
+ * `directive` : the name of the directive that can be used to set the value as a hidden reference; we can discuss whether, for pre- or user-defined types, it being undef means no directive or a default directive matching the attribute name would be defined.
+ * `linkdirective` : the name of the directive that can be used for a visible reference; no such directive would be defined by default
+ * `linktype` : link type for (hidden and visible) references
+ * `linkbase` : akin to the tagbase parameter
+ * `queries` : list of template queries this type/attribute/field/whatever is exposed to
+
+Where this approach is limiting is on the kind of data that is passed to (template) queries. The value of the metadata fields might need some massaging (e.g. compare how tags are passed to tags queries vs cateogires queries). I have problems on picturing an easy way to make this possible user-side (i.e. via templates and not in Perl modules). Suggestions welcome.