How deeply does ASP.NET Core in Action, 3e cover @addTagHelper directive?

Explains explicit and wildcard assembly registration, but does not develop Tag Helper implementation internals.

@addTagHelper directive

As explained in ASP.NET Core in Action, 3e

The @addTagHelper directive is a Razor directive that registers Tag Helpers for use in Razor files.

The @addTagHelper directive registers custom Tag Helpers for use in Razor views, partial views, and layouts. Place it in _ViewImports.cshtml so the registration applies throughout the relevant Razor files. section 32.1.1

Choose the registration form that matches the scope you need:

Register one Tag Helper by specifying its fully qualified type and assembly: @addTagHelper CustomTagHelpers.SystemInfoTagHelper, CustomTagHelpers. section 32.1.1
Register every Tag Helper in an assembly with wildcard syntax: @addTagHelper *, CustomTagHelpers. section 32.1.1
If IntelliSense is missing or Tag Helpers do not appear with Visual Studio’s Tag Helper styling, check the _ViewImports.cshtml registration. section 32.1.1

Registering custom Tag Helpers

A custom SystemInfoTagHelper can be made available with an explicit registration: @addTagHelper CustomTagHelpers.SystemInfoTagHelper, CustomTagHelpers. A wildcard registration instead enables all Tag Helpers from that assembly. After registration, Razor markup such as <system-info></system-info> can use the helper. section 32.1.1 section 32.1.2

How ASP.NET Core in Action, 3e covers it

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Related concepts

Tag Helpersconfigures · Tag Helpers are ASP.NET Core components that process HTML-like elements during Razor view or page rendering.
_ViewImports.cshtmlpart of · _ViewImports.cshtml is a Razor file whose namespaces and directives are implicitly available to views and pages in its directory scope.
wildcardconfigured by · A wildcard is a pattern symbol or expression that matches unspecified or variable characters, values, names, types, or path segments.

This explainer was generated by Manning's knowledge graph from the text of ASP.NET Core in Action, 3e. The section links point to the parts of the book it draws on.