diff --git a/CHANGELOG.md b/CHANGELOG.md
index 01f734a9..ea7a1ef5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,12 +6,15 @@
 - Expanding the value of a graph container which is already a graph object
   generates a recursive graph object.
 - Compacting multiple nodes in a graph container places them in `@included`.
+- Indexing on "@type" requires "@type" to be either "@id" or "@vocab",
+  and defaults to "@id".
 
 ### Changed
 - Default processing mode changed to json-ld-1.1. Allows a 1.1 context to be
   used after non-1.1 contexts.
-- `@vocab` can be relative or a Compact IRI in 1.1, resolved against either a previous `@vocab`,
-  `@base` or document base.
+- Indexing on an arbitrary property, not just "@index".
+- `@vocab` can be relative or a Compact IRI in 1.1, resolved against either
+  a previous `@vocab`, `@base` or document base.
 - Better checking of absolute IRIs.
 - Terms that begin with a ':' are not considered absolute or compact IRIs.
 - Don't use terms with `"@prefix": false` or expanded term definitions to construct compact IRIs.
diff --git a/lib/compact.js b/lib/compact.js
index 48a9ec08..66369c18 100644
--- a/lib/compact.js
+++ b/lib/compact.js
@@ -521,7 +521,33 @@ api.compact = async ({
             }
             key = expandedItem['@language'];
           } else if(container.includes('@index')) {
-            key = expandedItem['@index'];
+            const indexKey = _getContextValue(
+              activeCtx, itemActiveProperty, '@index') || '@index';
+            const containerKey = api.compactIri(
+              {activeCtx, iri: indexKey, vocab: true});
+            if(indexKey === '@index') {
+              key = expandedItem['@index'];
+              delete compactedItem[containerKey];
+            } else {
+              let others;
+              [key, ...others] = _asArray(compactedItem[indexKey] || []);
+              if(!_isString(key)) {
+                // Will use @none if it isn't a string.
+                key = null;
+              } else {
+                switch(others.length) {
+                  case 0:
+                    delete compactedItem[indexKey];
+                    break;
+                  case 1:
+                    compactedItem[indexKey] = others[0];
+                    break;
+                  default:
+                    compactedItem[indexKey] = others;
+                    break;
+                }
+              }
+            }
           } else if(container.includes('@id')) {
             const idKey = api.compactIri({activeCtx, iri: '@id', vocab: true});
             key = compactedItem[idKey];
@@ -545,6 +571,19 @@ api.compact = async ({
                 compactedItem[typeKey] = types;
                 break;
             }
+
+            // If compactedItem contains a single entry
+            // whose key maps to @id, recompact without @type
+            if(Object.keys(compactedItem).length === 1 &&
+              '@id' in expandedItem) {
+              compactedItem = await api.compact({
+                activeCtx,
+                activeProperty: itemActiveProperty,
+                element: {'@id': expandedItem['@id']},
+                options,
+                compactionMap
+              });
+            }
           }
 
           // if compacting this value which has no key, index on @none
@@ -1063,7 +1102,7 @@ function _selectTerm(
 
   // determine prefs for @id based on whether or not value compacts to a term
   if((typeOrLanguageValue === '@id' || typeOrLanguageValue === '@reverse') &&
-    _isSubjectReference(value)) {
+    _isObject(value) && '@id' in value) {
     // prefer @reverse first
     if(typeOrLanguageValue === '@reverse') {
       prefs.push('@reverse');
diff --git a/lib/context.js b/lib/context.js
index e151fb47..bb33d82f 100644
--- a/lib/context.js
+++ b/lib/context.js
@@ -375,7 +375,7 @@ api.createTermDefinition = (
 
   // JSON-LD 1.1 support
   if(api.processingMode(activeCtx, 1.1)) {
-    validKeys.push('@context', '@nest', '@prefix', '@protected');
+    validKeys.push('@context', '@index', '@nest', '@prefix', '@protected');
   }
 
   for(const kw in value) {
@@ -560,6 +560,21 @@ api.createTermDefinition = (
         // otherwise, container may also include @set
         isValid &= container.length <= (hasSet ? 2 : 1);
       }
+
+      if(container.includes('@type')) {
+        // If mapping does not have an @type,
+        // set it to @id
+        mapping['@type'] = mapping['@type'] || '@id';
+
+        // type mapping must be either @id or @vocab
+        if(!['@id', '@vocab'].includes(mapping['@type'])) {
+          throw new JsonLdError(
+            'Invalid JSON-LD syntax; container: @type requires @type to be ' +
+            '@id or @vocab.',
+            'jsonld.SyntaxError',
+            {code: 'invalid type mapping', context: localCtx});
+        }
+      }
     } else {
       // in JSON-LD 1.0, container must not be an array (it must be a string,
       // which is one of the validContainers)
@@ -595,6 +610,23 @@ api.createTermDefinition = (
     mapping['@container'] = container;
   }
 
+  // property indexing
+  if('@index' in value) {
+    if(!('@container' in value) || !mapping['@container'].includes('@index')) {
+      throw new JsonLdError(
+        'Invalid JSON-LD syntax; @index without @index in @container: ' +
+        `"${value['@index']}" on term "${term}".`, 'jsonld.SyntaxError',
+        {code: 'invalid term definition', context: localCtx});
+    }
+    if(!_isString(value['@index']) || value['@index'].indexOf('@') === 0) {
+      throw new JsonLdError(
+        'Invalid JSON-LD syntax; @index must expand to an IRI: ' +
+        `"${value['@index']}" on term "${term}".`, 'jsonld.SyntaxError',
+        {code: 'invalid term definition', context: localCtx});
+    }
+    mapping['@index'] = value['@index'];
+  }
+
   // scoped contexts
   if('@context' in value) {
     mapping['@context'] = value['@context'];
diff --git a/lib/expand.js b/lib/expand.js
index 91c3d8e0..87bf0289 100644
--- a/lib/expand.js
+++ b/lib/expand.js
@@ -610,6 +610,10 @@ async function _expandObject({
     } else if(container.includes('@index') && _isObject(value)) {
       // handle index container (skip if value is not an object)
       const asGraph = container.includes('@graph');
+      const indexKey = _getContextValue(termCtx, key, '@index') || '@index';
+      const propertyIndex = indexKey !== '@index' &&
+        _expandIri(activeCtx, indexKey, {vocab: true}, options);
+
       expandedValue = await _expandIndexMap({
         activeCtx: termCtx,
         options,
@@ -617,7 +621,8 @@ async function _expandObject({
         value,
         expansionMap,
         asGraph,
-        indexKey: '@index'
+        indexKey,
+        propertyIndex
       });
     } else if(container.includes('@id') && _isObject(value)) {
       // handle id container (skip if value is not an object)
@@ -890,7 +895,7 @@ function _expandLanguageMap(activeCtx, languageMap, options) {
 
 async function _expandIndexMap(
   {activeCtx, options, activeProperty, value, expansionMap, asGraph,
-    indexKey}) {
+    indexKey, propertyIndex}) {
   const rval = [];
   const keys = Object.keys(value).sort();
   const isTypeIndex = indexKey === '@type';
@@ -913,15 +918,6 @@ async function _expandIndexMap(
       val = [val];
     }
 
-    // expand for @type, but also for @none
-    const expandedKey = _expandIri(activeCtx, key, {vocab: true}, options);
-    if(indexKey === '@id') {
-      // expand document relative
-      key = _expandIri(activeCtx, key, {base: true}, options);
-    } else if(isTypeIndex) {
-      key = expandedKey;
-    }
-
     val = await api.expand({
       activeCtx,
       activeProperty,
@@ -931,6 +927,27 @@ async function _expandIndexMap(
       insideIndex: true,
       expansionMap
     });
+
+    // expand for @type, but also for @none
+    let expandedKey;
+    if(propertyIndex) {
+      if(key === '@none') {
+        expandedKey = '@none';
+      } else {
+        expandedKey = _expandValue(
+          {activeCtx, activeProperty: indexKey, value: key, options});
+      }
+    } else {
+      expandedKey = _expandIri(activeCtx, key, {vocab: true}, options);
+    }
+
+    if(indexKey === '@id') {
+      // expand document relative
+      key = _expandIri(activeCtx, key, {base: true}, options);
+    } else if(isTypeIndex) {
+      key = expandedKey;
+    }
+
     for(let item of val) {
       // If this is also a @graph container, turn items into graphs
       if(asGraph && !_isGraph(item)) {
@@ -944,6 +961,23 @@ async function _expandIndexMap(
         } else {
           item['@type'] = [key];
         }
+      } else if(_isValue(item) &&
+        !['@language', '@type', '@index'].includes(indexKey)) {
+        throw new JsonLdError(
+          'Invalid JSON-LD syntax; Attempt to add illegal key to value ' +
+          `object: "${indexKey}".`,
+          'jsonld.SyntaxError',
+          {code: 'invalid value object', value: item});
+      } else if(propertyIndex) {
+        // index is a property to be expanded, and values interpreted for that
+        // property
+        if(expandedKey !== '@none') {
+          // expand key as a value
+          _addValue(item, propertyIndex, expandedKey, {
+            propertyIsArray: true,
+            prependValue: true
+          });
+        }
       } else if(expandedKey !== '@none' && !(indexKey in item)) {
         item[indexKey] = key;
       }
diff --git a/lib/util.js b/lib/util.js
index 2baaa2e5..b250d51d 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -234,6 +234,8 @@ api.hasValue = (subject, property, value) => {
  *          an array (lists) (default: false).
  *        [allowDuplicate] true to allow duplicates, false not to (uses a
  *          simple shallow comparison of subject ID or value) (default: true).
+ *        [prependValue] false to prepend value to any existing values.
+ *          (default: false)
  */
 api.addValue = (subject, property, value, options) => {
   options = options || {};
@@ -246,6 +248,9 @@ api.addValue = (subject, property, value, options) => {
   if(!('allowDuplicate' in options)) {
     options.allowDuplicate = true;
   }
+  if(!('prependValue' in options)) {
+    options.prependValue = false;
+  }
 
   if(options.valueIsArray) {
     subject[property] = value;
@@ -254,6 +259,10 @@ api.addValue = (subject, property, value, options) => {
       !subject.hasOwnProperty(property)) {
       subject[property] = [];
     }
+    if(options.prependValue) {
+      value = value.concat(subject[property]);
+      subject[property] = [];
+    }
     for(let i = 0; i < value.length; ++i) {
       api.addValue(subject, property, value[i], options);
     }
@@ -270,7 +279,11 @@ api.addValue = (subject, property, value, options) => {
 
     // add new value
     if(!hasValue) {
-      subject[property].push(value);
+      if(options.prependValue) {
+        subject[property].unshift(value);
+      } else {
+        subject[property].push(value);
+      }
     }
   } else {
     // add new value as set or single value
diff --git a/tests/test-common.js b/tests/test-common.js
index 729a8135..5781d7f5 100644
--- a/tests/test-common.js
+++ b/tests/test-common.js
@@ -39,13 +39,8 @@ const TEST_TYPES = {
         /compact-manifest.jsonld#ttn01$/,
         /compact-manifest.jsonld#ttn02$/,
         /compact-manifest.jsonld#ttn03$/,
-        // property-valued indexes
-        /compact-manifest.jsonld#tpi01$/,
-        /compact-manifest.jsonld#tpi02$/,
-        /compact-manifest.jsonld#tpi03$/,
-        /compact-manifest.jsonld#tpi04$/,
-        /compact-manifest.jsonld#tpi05$/,
-        /compact-manifest.jsonld#tpi06$/,
+        // IRI confusion
+        /compact-manifest.jsonld#te002$/,
         // @propogate
         /compact-manifest.jsonld#tc026$/,
         /compact-manifest.jsonld#tc027$/,
@@ -55,10 +50,6 @@ const TEST_TYPES = {
         /compact-manifest.jsonld#tin03$/,
         /compact-manifest.jsonld#tin04$/,
         /compact-manifest.jsonld#tin05$/,
-        // index on @type
-        /compact-manifest.jsonld#tm020$/,
-        /compact-manifest.jsonld#tm021$/,
-        /compact-manifest.jsonld#tm022$/,
         // context values
         /compact-manifest.jsonld#ts001$/,
         /compact-manifest.jsonld#ts002$/,
@@ -142,18 +133,6 @@ const TEST_TYPES = {
         /expand-manifest.jsonld#thc05$/,
         // @type: @none
         /expand-manifest.jsonld#ttn02$/,
-        // property index maps
-        /expand-manifest.jsonld#tpi01$/,
-        /expand-manifest.jsonld#tpi02$/,
-        /expand-manifest.jsonld#tpi03$/,
-        /expand-manifest.jsonld#tpi04$/,
-        /expand-manifest.jsonld#tpi05$/,
-        /expand-manifest.jsonld#tpi06$/,
-        /expand-manifest.jsonld#tpi07$/,
-        /expand-manifest.jsonld#tpi08$/,
-        /expand-manifest.jsonld#tpi09$/,
-        /expand-manifest.jsonld#tpi10$/,
-        /expand-manifest.jsonld#tpi11$/,
         // misc
         /expand-manifest.jsonld#te043$/,
         /expand-manifest.jsonld#te044$/,
@@ -203,9 +182,6 @@ const TEST_TYPES = {
         /expand-manifest.jsonld#tin07$/,
         /expand-manifest.jsonld#tin08$/,
         /expand-manifest.jsonld#tin09$/,
-        // index on @type
-        /expand-manifest.jsonld#tm017$/,
-        /expand-manifest.jsonld#tm020$/,
         // @nest
         /expand-manifest.jsonld#tn008$/,
         // keywords
@@ -473,9 +449,6 @@ const TEST_TYPES = {
         /toRdf-manifest.jsonld#tin04$/,
         /toRdf-manifest.jsonld#tin05$/,
         /toRdf-manifest.jsonld#tin06$/,
-        // index on @type
-        /toRdf-manifest.jsonld#tm017$/,
-        /toRdf-manifest.jsonld#tm020$/,
         // @next
         /toRdf-manifest.jsonld#tn008$/,
         // keywords