diff --git a/src/utils.jl b/src/utils.jl
index cd7bb414..324aa2cb 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -344,7 +344,9 @@ const _scale_base = Dict{Symbol, Real}(
 
 function _heatmap_edges(v::AVec, isedges::Bool = false)
   length(v) == 1 && return v[1] .+ [-0.5, 0.5]
-  if isedges return v end
+  if isedges return v end 
+  # `isedges = true` means that v is a vector which already describes edges 
+  # and does not need to be extended.
   vmin, vmax = ignorenan_extrema(v)
   extra_min = (v[2] - v[1]) / 2
   extra_max = (v[end] - v[end - 1]) / 2
@@ -352,24 +354,24 @@ function _heatmap_edges(v::AVec, isedges::Bool = false)
 end
 
 "create an (n+1) list of the outsides of heatmap rectangles"
-function heatmap_edges(v::AVec, scale::Symbol = :identity; isedges::Bool = false)
+function heatmap_edges(v::AVec, scale::Symbol = :identity, isedges::Bool = false)
   f, invf = scalefunc(scale), invscalefunc(scale)
   map(invf, _heatmap_edges(map(f,v), isedges))
 end
 
 function heatmap_edges(x::AVec, xscale::Symbol, y::AVec, yscale::Symbol, z_size::Tuple{Int, Int})
     nx, ny = length(x), length(y)
-    # use_midpoints = z_size == (ny, nx) # This fails some tests, but would actually be 
+    # ismidpoints = z_size == (ny, nx) # This fails some tests, but would actually be 
     # the correct check, since (4, 3) != (3, 4) and a missleading plot is produced.
-    use_midpoints = prod(z_size) == (ny * nx) 
-    use_edges = z_size == (ny - 1, nx - 1)
-    if !use_midpoints && !use_edges
+    ismidpoints = prod(z_size) == (ny * nx) 
+    isedges = z_size == (ny - 1, nx - 1)
+    if !ismidpoints && !isedges
         error("""Length of x & y does not match the size of z. 
                 Must be either `size(z) == (length(y), length(x))` (x & y define midpoints)
                 or `size(z) == (length(y)+1, length(x)+1))` (x & y define edges).""")
     end
-    x, y = heatmap_edges(x, xscale; isedges = use_edges), 
-           heatmap_edges(y, yscale; isedges = use_edges)
+    x, y = heatmap_edges(x, xscale, isedges), 
+           heatmap_edges(y, yscale, isedges)
     return x, y
 end