diff --git a/package.json b/package.json
index d422e13f..59c84445 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "proskomma",
-  "version": "0.7.13",
+  "version": "0.7.14",
   "description": "A Scripture Runtime Engine",
   "main": "dist/index.js",
   "files": [
diff --git a/src/index.js b/src/index.js
index 2ebdc9fc..8f9163dc 100644
--- a/src/index.js
+++ b/src/index.js
@@ -38,7 +38,7 @@ const executableSchema =
   });
 
 class Proskomma {
-  constructor() {
+  constructor(selectors) {
     this.processorId = generateId();
     this.documents = {};
     this.docSetsBySelector = {};
@@ -53,7 +53,7 @@ class Proskomma {
       introHeading: [],
     };
     this.emptyBlocks = [];
-    this.selectors = [
+    this.selectors = selectors || [
       {
         name: 'lang',
         type: 'string',
@@ -64,6 +64,7 @@ class Proskomma {
         type: 'string',
       },
     ];
+    this.validateSelectorSpec(this.selectors);
     this.mutex = new Mutex();
     this.nextPeriph = 0;
     this.nextTable = 0;
@@ -146,6 +147,28 @@ class Proskomma {
     }
   }
 
+  validateSelectorSpec(spec) {
+    for (const specElement of spec) {
+      if (!specElement['name']) {
+        throw new Error(`name not found in selector spec element '${JSON.stringify(specElement)}'`);
+      }
+
+      if (!specElement['type']) {
+        throw new Error(`type not found in selector spec element '${JSON.stringify(specElement)}'`);
+      }
+
+      if (!['string', 'integer'].includes(specElement.type)) {
+        throw new Error(`Type for spec element must be string or number, not ${specElement.type}`);
+      }
+
+      for (const selectorKey of Object.keys(specElement)) {
+        if (!['name', 'type', 'regex', 'min', 'max', 'enum'].includes(selectorKey)) {
+          throw new Error(`Unexpected key '${selectorKey}' in selectorSpec`);
+        }
+      }
+    }
+  }
+
   selectorString(docSetSelectors) {
     // In root so it can be easily subclassed
     return this.selectors.map(s => s.name).map(n => `${docSetSelectors[n]}`).join('_');
@@ -326,7 +349,7 @@ class Proskomma {
       return false;
     }
 
-    for (const docId of Object.entries(this.documents).filter(([id, doc]) => doc.docSetId === docSetId).map(tup => tup[0])) {
+    for (const docId of Object.entries(this.documents).filter(tup => tup[1].docSetId === docSetId).map(tup => tup[0])) {
       this.deleteDocument(docSetId, docId, false, false);
     }
 
diff --git a/test/code/custom.cjs b/test/code/custom.cjs
index 499cc195..74593482 100644
--- a/test/code/custom.cjs
+++ b/test/code/custom.cjs
@@ -87,4 +87,37 @@ test(
       console.log(err);
     }
   },
-);
\ No newline at end of file
+);
+
+test(
+  'Specify Selector Spec (${testGroup})',
+  async function (t) {
+    try {
+      t.plan(2);
+      t.doesNotThrow(() => new Proskomma([
+        {
+          name: 'lang',
+          type: 'string',
+          regex: '[a-z]{3}',
+        },
+        {
+          name: 'abbr',
+          type: 'string',
+        },
+      ]));
+      t.throws(() => new Proskomma([
+        {
+          name: 'lang',
+          type: 'stringz',
+          regex: '[a-z]{3}',
+        },
+        {
+          name: 'abbr',
+          type: 'string',
+        },
+      ]), /stringz/);
+    } catch (err) {
+      console.log(err);
+    }
+  },
+)
diff --git a/test/code/mutate_delete.cjs b/test/code/mutate_delete.cjs
index 48a2926c..69bbef92 100644
--- a/test/code/mutate_delete.cjs
+++ b/test/code/mutate_delete.cjs
@@ -47,7 +47,7 @@ test(
   `Reload Deleted DocSet (${testGroup})`,
   async function (t) {
     try {
-      t.plan(2);
+      t.plan(3);
       const selectors = {
         lang: 'eng',
         abbr: 'ust',
@@ -57,9 +57,10 @@ test(
       let result = await pk.gqlQuery(query);
       query = `mutation { deleteDocSet(docSetId: "${result.data.docSets[0].id}") }`;
       result = await pk.gqlQuery(query);
-      query = '{ docSets { id } }';
+      query = '{ docSets { id } nDocuments}';
       result = await pk.gqlQuery(query);
       t.equal(result.data.docSets.length, 0);
+      t.equal(result.data.nDocuments, 0);
       const content = fse.readFileSync(path.resolve(__dirname, '../test_data/usx/web_rut.usx'));
 
       t.doesNotThrow(