diff --git a/structs.scad b/structs.scad
index bb0986c..1c9b2f7 100644
--- a/structs.scad
+++ b/structs.scad
@@ -12,99 +12,113 @@
 // Section: struct operations
 //
 // A struct is a data structure that associates arbitrary keywords (of any type) with values (of any type).
-// Structures are implemented as lists of [keyword, value] pairs.  
+// Structures are implemented as lists of [keyword, value] pairs.
 //
 // An empty list `[]` is an empty structure and can be used wherever a structure input is required.
 
 // Function: struct_set()
 // Usage:
-//    struct_set(struct, keyword, value, [grow])
-//    struct_set(struct, [keyword1, value1, keyword2, value2, ...], [grow])
+//   struct_set(struct, keyword, value, [grow])
+//   struct_set(struct, [keyword1, value1, keyword2, value2, ...], [grow])
 // Description:
-//    Sets the keyword(s) in the structure to the specified value(s), returning a new updated structure.  If a keyword
-//    exists its value is changed, otherwise the keyword is added to the structure.  If grow is set to false then
-//    it is an error to set a keyword not already defined in the structure.  If you specify the same keyword twice
-//    that is also an error.  If speed matters, use the first form with scalars rather than the list form: this is
-//    about thirty times faster. 
+//   Sets the keyword(s) in the structure to the specified value(s), returning a new updated structure.  If a keyword
+//   exists its value is changed, otherwise the keyword is added to the structure.  If grow is set to false then
+//   it is an error to set a keyword not already defined in the structure.  If you specify the same keyword twice
+//   that is also an error.  If speed matters, use the first form with scalars rather than the list form: this is
+//   about thirty times faster.
 // Arguments:
-//    struct = input structure
-//    keyword = keyword to set
-//    value = value to set the keyword to
-//    grow = Set to true to allow structure to grow, or false for new keywords to generate an error.  Default: true
+//   struct = Input structure.
+//   keyword = Keyword to set.
+//   value = Value to set the keyword to.
+//   grow = Set to true to allow structure to grow, or false for new keywords to generate an error.  Default: true
 function struct_set(struct, keyword, value=undef, grow=true) =
-     !is_list(keyword) ?
-        let(ind=search([keyword],struct,1,0)[0])
-        (ind==[] ? assert(grow,str("Unknown keyword \"",keyword))
-                   concat(struct, [[keyword,value]]) :
-               list_set(struct, [ind], [[keyword,value]])) :
-               _parse_pairs(struct,keyword,grow);
+	!is_list(keyword)? (
+		let( ind=search([keyword],struct,1,0)[0] )
+		ind==[]? (
+			assert(grow,str("Unknown keyword \"",keyword))
+			concat(struct, [[keyword,value]])
+		) : list_set(struct, [ind], [[keyword,value]])
+	) : _parse_pairs(struct,keyword,grow);
+
 
 function _parse_pairs(spec, input, grow=true, index=0, result=undef) =
-     assert(len(input)%2==0,"Odd number of entries in [keyword,value] pair list")
-     let( result = result==undef ? spec : result)
-     index == len(input) ? result :  
-   _parse_pairs(spec,input,grow,index+2,struct_set(result, input[index], input[index+1],grow));
+	assert(len(input)%2==0,"Odd number of entries in [keyword,value] pair list")
+	let( result = result==undef ? spec : result)
+	index == len(input) ? result :
+	_parse_pairs(spec,input,grow,index+2,struct_set(result, input[index], input[index+1],grow));
+
 
 // Function: struct_remove()
 // Usage:
-//    struct_remove(struct, keyword)
+//   struct_remove(struct, keyword)
 // Description:
-//    Remove keyword or keyword list from a structure
+//   Remove keyword or keyword list from a structure
 // Arguments:
-//    struct = input structure
-//    keyword = a single string (keyword) or list of strings (keywords) to remove
+//   struct = input structure
+//   keyword = a single string (keyword) or list of strings (keywords) to remove
 function struct_remove(struct, keyword) =
-    is_string(keyword)? struct_remove(struct, [keyword]) :
-    let(ind = search(keyword, struct))
-     list_remove(struct, ind);
+	is_string(keyword)? struct_remove(struct, [keyword]) :
+	let(ind = search(keyword, struct))
+	list_remove(struct, ind);
+
 
 // Function: struct_val()
 // Usage:
-//    struct_val(struct,keyword)
+//   struct_val(struct,keyword)
 // Description:
-//    Returns the value for the specified keyword in the structure, or undef if the keyword is not present
+//   Returns the value for the specified keyword in the structure, or undef if the keyword is not present
 // Arguments:
-//    struct = input structure
-//    keyword = keyword whose value to return
+//   struct = input structure
+//   keyword = keyword whose value to return
 function struct_val(struct,keyword) =
-     assert(is_def(keyword),"keyword is missing")
-     let(ind = search([keyword],struct)[0])
-     ind == [] ? undef : struct[ind][1];
+	assert(is_def(keyword),"keyword is missing")
+	let(ind = search([keyword],struct)[0])
+	ind == [] ? undef : struct[ind][1];
+
 
 // Function: struct_keys()
 // Usage:
-//    struct_keys(struct)
+//   keys = struct_keys(struct)
 // Description:
-//    Returns a list of the keys in a structure
+//   Returns a list of the keys in a structure
 // Arguments:
-//    struct = input structure
+//   struct = input structure
 function struct_keys(struct) =
-     [for(entry=struct) entry[0]];
+	[for(entry=struct) entry[0]];
 
-// Function&Module struct_echo()
+
+// Function&Module: struct_echo()
 // Usage:
-//    struct_echo(struct, [name])
+//   struct_echo(struct, [name])
 // Description:
-//    Displays a list of structure keywords and values, one pair per line, for easier reading.
+//   Displays a list of structure keywords and values, one pair per line, for easier reading.
 // Arguments:
-//    struct = input structure
-//    name = optional structure name to list at the top of the output.  Default: ""
+//   struct = input structure
+//   name = optional structure name to list at the top of the output.  Default: ""
 function struct_echo(struct,name="") =
-   let( keylist = [for(entry=struct) str("  ",entry[0],": ",entry[1],"\n")])
-   echo(str("\nStructure ",name,"\n",str_join(keylist)))
-   undef;
+	let( keylist = [for(entry=struct) str("  ",entry[0],": ",entry[1],"\n")])
+	echo(str("\nStructure ",name,"\n",str_join(keylist)))
+	undef;
 
 module struct_echo(struct,name="") {
-   dummy = struct_echo(struct,name);
+	dummy = struct_echo(struct,name);
 }
 
-// Function is_struct()
+
+// Function: is_struct()
 // Usage:
-//    is_struct(struct)
-// Description: Returns true if the input has the form of a structure, false otherwise.  
-function is_struct(struct, ind=0) =
-    is_list(struct) && (
-	struct == [] ||
-	let(dim = array_dim(struct))
-	len(dim)==2 && dim[1]==2
-    );
+//   is_struct(struct)
+// Description:
+//   Returns true if the input has the form of a structure, false otherwise.
+function is_struct(x) =
+	is_list(x) && [
+		for (xx=x) if(
+			!is_list(xx) ||
+			len(xx) != 2 ||
+			!is_string(xx[0])
+		) 1
+	] == [];
+
+
+
+// vim: noexpandtab tabstop=4 shiftwidth=4 softtabstop=4 nowrap
diff --git a/version.scad b/version.scad
index 4b407fa..9cfb5eb 100644
--- a/version.scad
+++ b/version.scad
@@ -8,7 +8,7 @@
 //////////////////////////////////////////////////////////////////////
 
 
-BOSL_VERSION = [2,0,310];
+BOSL_VERSION = [2,0,311];
 
 
 // Section: BOSL Library Version Functions