Setup Mkdocs (#7)

* Compile docs with Mkdocs

* Add info about project

docs/dotnet/asp.net/razor-syntax.md

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+# [Razor Syntax](https://docs.microsoft.com/en-us/aspnet/core/mvc/views/razor)
+
+## Markup
+
+```cs
+@page  // set this as razor page
+
+@model <App>.Models.Entity  // if MVC set type of elements passed to the view 
+@model <Page>Model  // if Razor page set underlying class
+
+@* razor comment *@
+
+// substitute @variable with it's value
+<tag>@variable</tag>
+
+@{
+    // razor code block
+    // can contain C# or HTML
+
+    Model  // access to passed @model (MVC)
+}
+
+@if (condition) { }
+
+@for (init, condition, iteration) { }
+
+@Model.Property  // display Property value (MVC)
+```
+
+---
+
+## Tag Helpers (ASP.NET Core)
+
+**Tag helpers** are reusable components for automating the generation of HTML in Razor Pages. Tag helpers target specific HTML tags.
+
+Example:
+
+```html
+<!-- tag helpers for a lin in ASP.NET MVC -->
+<a class="nav-link text-dark" asp-area="" asp-controller="Home" asp-action="Index">Home</a>
+```
+
+### Managing Tag Helpers
+
+The `@addTagHelper` directive makes Tag Helpers available to the view. Generally, the view file is `Pages/_ViewImports.cshtml`, which by default is inherited by all files in the `Pages` folder and subfolders, making Tag Helpers available.
+
+```cs
+@using <App>
+@namespace <App>.Pages  // or <Project>.Models
+@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+```
+
+The first parameter after `@addTagHelper` specifies the Tag Helpers to load (`*` for all Tag Helpers), and the second parameter (e.g. `Microsoft.AspNetCore.Mvc.TagHelpers`) specifies the assembly containing the Tag Helpers.
+`Microsoft.AspNetCore.Mvc.TagHelpers` is the assembly for the built-in ASP.NET Core Tag Helpers.
+
+#### Opting out of individual elements
+
+It's possible to disable a Tag Helper at the element level with the Tag Helper opt-out character (`!`)
+
+```cshtml
+<!-- disable email validation -->
+<!span asp-validation-for="Email" ></!span>
+```
+
+### Explicit Tag Helpers
+
+The `@tagHelperPrefix` directive allows to specify a tag prefix string to enable Tag Helper support and to make Tag Helper usage explicit.
+
+```cshtml
+@tagHelpersPrefix th:
+```
+
+### Important Tag Helpers (`asp-`) & HTML Helpers (`@Html`)
+
+[Understanding Html Helpers](https://stephenwalther.com/archive/2009/03/03/chapter-6-understanding-html-helpers)
+
+```cs
+@model <App>.Models.Entity
+
+// Display the name of the property
+@Html.DisplayNameFor(model => model.EntityProp)
+@nameof(Model.EntityProp)
+
+// Display the value of the property
+@Html.DisplayFor(model => model.EntityProp)
+@Model.EntityProp
+
+<from>
+    // use the property as the label, eventually w/ [DisplayName("...")]
+    <label asp-for="EntityProp"></label>
+    @Html.LabelFor()
+
+    // automatically set the value at form compilation and submission
+    <input asp-for="EntityProp"/>
+    @Html.EditorFor()
+</from>
+
+// route config is {Controller}/{Action}/{Id?}
+<a asp-controller="<Controller>" asp-action="<Action>">Link</a>  // link to /Controller/Action
+<a asp-controller="<Controller>" asp-action="<Action>" asp-route-Id="@model.Id">Link</a>  // link to /Controller/Action/Id
+@Html.ActionLink("<Link Text>", "<Action>", "<Controller>", new { @HTmlAttribute = value, Id = value }) // link to /Controller/Action/Id
+
+// link to /Controller/Action?queryParameter=value
+@Html.ActionLink("<Link Text>", "<Action>", "<Controller>", new { @HTmlAttribute = value, queryParameter = value })
+<a asp-controller="<Controller>" asp-action="<Action>" asp-route-queryParameter="value">Link</a>  // asp-route-* for query strings
+```
+
+### [Select Tag Helper](https://docs.microsoft.com/en-us/aspnet/core/mvc/views/working-with-forms)
+
+[StackOverflow](https://stackoverflow.com/a/34624217)
+[SelectList Docs](https://docs.microsoft.com/en-us/dotnet/api/system.web.mvc.selectlist)
+
+In `ViewModel.cs`:
+
+```cs
+class ViewModel 
+{
+    public int EntityId { get; set; }  // value selected in form ends up here
+
+    // object has numeric id and other props
+    public SelectList Entities = new()
+
+    public ViewModel(){ }  // parameterless constructor (NEEDED)
+}
+```
+
+In `View.cs`
+
+```cs
+@model ViewModel
+
+<form asp-controller="Controller" asp-action="PostAction">
+
+    <select asp-for"EntityId" asp-items="Model.Entities">
+    </select>
+
+    <button type="submit">Send<button>
+</form>
+```
+
+In `Controller.cs`:
+
+```cs
+public IActionResult GetAction()
+{
+    var vm = new ViewModel();
+
+    vm.Entities = new SelectList(_context.Entities, "Id", "Text");  // fill SelectList
+    vm.EntityId = value;  // set selected option (OPTIONAL)
+    
+    return View(vm);
+}
+
+
+[HttpPost]
+public IActionResult PostAction(ViewModel)
+{
+    if(ModelState.IsValid)
+    {
+        // extract info from view model
+        // save to db
+    }
+}
+```