diff --git a/CHANGELOG.md b/CHANGELOG.md
index 41c12027..dc800084 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+v0.6.100
+* Added -frame command, for creating a rectangular map frame layer with a defined display size. Used to set SVG output size and on-screen symbol scale.
+* Added -o no-null-props option, which uses "properties":{} instead of "properties":null when outputting GeoJSON features with no attribute data.
+* Added support for sub-pixel sizes of pattern fills like hatches and dots (see the -style fill-effect= option).
+* Bug fixes
+
 v0.6.99
 * Bug fixes
 
diff --git a/REFERENCE.md b/REFERENCE.md
index d71f4237..9f7cee68 100644
--- a/REFERENCE.md
+++ b/REFERENCE.md
@@ -1,6 +1,6 @@
 # COMMAND REFERENCE
 
-This documentation applies to version 0.6.98 of mapshaper's command line program. Run `mapshaper -v` to check your version. For an introduction to the command line tool, read [this page](https://github.com/mbloch/mapshaper/wiki/Introduction-to-the-Command-Line-Tool) first.
+This documentation applies to version 0.6.100 of mapshaper's command line program. Run `mapshaper -v` to check your version. For an introduction to the command line tool, read [this page](https://github.com/mbloch/mapshaper/wiki/Introduction-to-the-Command-Line-Tool) first.
 
 ## Command line syntax
 
diff --git a/package-lock.json b/package-lock.json
index e2bd0b01..78713c90 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "mapshaper",
-  "version": "0.6.99",
+  "version": "0.6.100",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "mapshaper",
-      "version": "0.6.99",
+      "version": "0.6.100",
       "license": "MPL-2.0",
       "dependencies": {
         "@placemarkio/tokml": "^0.3.3",
diff --git a/package.json b/package.json
index 96cd0f40..80e6f2eb 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "mapshaper",
-  "version": "0.6.99",
+  "version": "0.6.100",
   "description": "A tool for editing vector datasets for mapping and GIS.",
   "keywords": [
     "shapefile",
diff --git a/src/commands/mapshaper-comment.mjs b/src/commands/mapshaper-comment.mjs
index 3db9f169..bd4bb565 100644
--- a/src/commands/mapshaper-comment.mjs
+++ b/src/commands/mapshaper-comment.mjs
@@ -1,3 +1,7 @@
 import cmd from '../mapshaper-cmd';
+import { verbose, message } from '../utils/mapshaper-logging';
 
-cmd.comment = function() {}; // no-op, so -comment doesn't trigger a parsing error
+cmd.comment = function(opts) {
+  // TODO: print the comment in verbose mode
+  // message('[comment]', opts.message);
+}; // no-op, so -comment doesn't trigger a parsing error
diff --git a/src/commands/mapshaper-rectangle.mjs b/src/commands/mapshaper-rectangle.mjs
index 3ca2155f..da99f756 100644
--- a/src/commands/mapshaper-rectangle.mjs
+++ b/src/commands/mapshaper-rectangle.mjs
@@ -57,6 +57,9 @@ cmd.rectangles = function(targetLyr, targetDataset, opts) {
   return outputLayers;
 };
 
+
+
+
 function shapesToBoxGeometries(lyr, dataset, opts) {
   var crsInfo = getDatasetCrsInfo(dataset);
   return lyr.shapes.map(function(shp) {
diff --git a/src/crs/mapshaper-projections.mjs b/src/crs/mapshaper-projections.mjs
index cfa8104f..0649928a 100644
--- a/src/crs/mapshaper-projections.mjs
+++ b/src/crs/mapshaper-projections.mjs
@@ -233,12 +233,12 @@ export function getDatasetCRS(dataset) {
   return getDatasetCrsInfo(dataset).crs;
 }
 
-export function requireDatasetsHaveCompatibleCRS(arr) {
+export function requireDatasetsHaveCompatibleCRS(arr, msg) {
   arr.reduce(function(memo, dataset) {
     var P = getDatasetCRS(dataset);
     if (memo && P) {
       if (isLatLngCRS(memo) != isLatLngCRS(P)) {
-        stop("Unable to combine projected and unprojected datasets");
+        stop(msg || "Unable to combine projected and unprojected datasets");
       }
     }
     return P || memo;
diff --git a/src/dataset/mapshaper-target-utils.mjs b/src/dataset/mapshaper-target-utils.mjs
index 9b2992d6..bf388992 100644
--- a/src/dataset/mapshaper-target-utils.mjs
+++ b/src/dataset/mapshaper-target-utils.mjs
@@ -13,6 +13,7 @@ export function expandCommandTargets(targets) {
 }
 
 
+
 export function findCommandTargets(layers, pattern, type) {
   var targets = [];
   var matches = findMatchingLayers(layers, pattern, true);
diff --git a/src/geom/mapshaper-units.mjs b/src/geom/mapshaper-units.mjs
index ccc2733c..37df99e4 100644
--- a/src/geom/mapshaper-units.mjs
+++ b/src/geom/mapshaper-units.mjs
@@ -35,7 +35,7 @@ export function parseSizeParam(p) {
   var px = units == 'in' && num * 72 ||
       units == 'cm' && Math.round(num * 28.3465) ||
       num;
-  if (px > 0 === false || !units) {
+  if (px >= 0 === false || !units) {
     stop('Invalid size:', str);
   }
   return px;
diff --git a/test/merge-layers-test.mjs b/test/merge-layers-test.mjs
index 69ec589a..d7a54404 100644
--- a/test/merge-layers-test.mjs
+++ b/test/merge-layers-test.mjs
@@ -77,7 +77,6 @@ describe('mapshaper-merge-layers.js', function () {
         done();
       });
 
-
     });
 
     it('handles empty layers', function(done) {