create selectable docs (#996)

docs/.vuepress/components/LimitSelectionQuantity.vue

@@ -0,0 +1,21 @@
+<template>
+  <v-select
+    multiple
+    placeholder="Choose up to 3 books!"
+    label="title"
+    v-model="selected"
+    :options="books"
+    :selectable="() => selected.length < 3"
+  />
+</template>
+<script>
+import books from '../data/books';
+export default {
+  data() {
+    return { selected: [] }
+  },
+  computed: {
+    books: () => books,
+  }
+}
+</script>

docs/.vuepress/components/UnselectableExample.vue

@@ -0,0 +1,16 @@
+<template>
+  <v-select
+    placeholder="Choose a book to read"
+    label="title"
+    :options="books"
+    :selectable="option => ! option.author.lastName.includes('Woodhouse')"
+  />
+</template>
+<script>
+import books from '../data/books';
+export default {
+  computed: {
+    books: () => books,
+  }
+}
+</script>

docs/.vuepress/config.js

@@ -118,6 +118,7 @@ module.exports = {
           collapsable: false,
           children: [
             ['guide/validation', 'Validation'],
+            ['guide/selectable', 'Limiting Selections'],
             ['guide/vuex', 'Vuex'],
             ['guide/ajax', 'AJAX'],
             ['guide/loops', 'Using in Loops'],

docs/guide/selectable.md

@@ -0,0 +1,44 @@
+## Selectable Prop <Badge text="v3.3.0+" />
+
+The `selectable` prop determines if an option is selectable or not. If `selectable` returns false
+for a given option, it will be displayed with a `vs__dropdown-option--disabled` class. The option
+will be disabled and unable to be selected. 
+
+```js
+selectable: {
+  type: Function,
+  /**
+   * @param {Object|String} option
+   * @return {boolean}
+   */
+  default: option => true,
+},
+```
+
+### Example
+
+Here `selectable` is used to prevent books by a certain author from being chosen. In this case,
+the options passed to the component are objects: 
+
+```json
+{ 
+    title: "Right Ho Jeeves", 
+    author: { firstName: "P.D", lastName: "Woodhouse" }, 
+}
+```
+
+This object will be passed to `selectable`, so we can check if the author should be selectable or not.
+
+<UnselectableExample />
+
+<<< @/.vuepress/components/UnselectableExample.vue{6}
+
+## Limiting the Number of Selections
+
+`selectable` can also be used a bit more creatively to limit the number selections that can be made 
+within the component. In this case, the user can select any author, but may only select a maximum
+of three books.
+
+<LimitSelectionQuantity />
+
+<<< @/.vuepress/components/LimitSelectionQuantity.vue{8}

src/components/Select.vue

@@ -229,10 +229,11 @@
       },
 
       /**
-       * Decides wether an option is selectable or not. Not selectable options
+       * Decides whether an option is selectable or not. Not selectable options
        * are displayed but disabled and cannot be selected.
        *
        * @type {Function}
+       * @since 3.3.0
        * @param {Object|String} option
        * @return {Boolean}
        */