Difference between revisions of "GUI Guidelines"

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(Buttons: Icon Naming Specification)
(Group into GUI elements and textual content)
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This page collects rules for the GUI. You should mind them while [[CodingStandard|coding]] or preparing translation ([[I18N]]).
 
This page collects rules for the GUI. You should mind them while [[CodingStandard|coding]] or preparing translation ([[I18N]]).
 +
 
= GUI Resolution =
 
= GUI Resolution =
 
The '''maximum size''' of ''all GUI elements'' restricts users to have at least the same resolution on their device to run GnuCash flawless. [https://bugs.gnucash.org/show_bug.cgi?id=797857 Bug 797857 - Edit->Preferences: Help/Close buttons unreachable] remembered us about this restriction.
 
The '''maximum size''' of ''all GUI elements'' restricts users to have at least the same resolution on their device to run GnuCash flawless. [https://bugs.gnucash.org/show_bug.cgi?id=797857 Bug 797857 - Edit->Preferences: Help/Close buttons unreachable] remembered us about this restriction.
Line 6: Line 7:
 
;GnuCash 2.x series: it was 800x600.
 
;GnuCash 2.x series: it was 800x600.
  
= Quoting in Strings =
+
= GUI Elements =
To get a unique appearance, the current team prefers ASCII double quotes <code>"</code> over single quotes <code>'</code> or non-ASCII characters.
+
 
;So ''developers'' should use in '''C''' etc.: <syntaxhighlight lang="C">
+
== Buttons and Icons ==
Msg= "Prefix \"Quotation\" Suffix."
+
For [https://docs.google.com/document/d/1KCVPoYQBqMbDP11tHPpjW6uaEHrvLUmcDPqKAppCY8o/pub GTK+ 3.10 Stock Items Deprecation] announced on [https://mail.gnome.org/archives/gtk-devel-list/2013-July/msg00000.html gtk-devel-list/2013-July] and the
</syntaxhighlight>
+
[https://docs.google.com/spreadsheets/d/1HavJQRPpMuq-N0GoN1wJR-9KEGXpKy3-NEPpZZkUGJY/pub?output=html Replacement Table] watch the current discussion starting with [https://lists.gnucash.org/pipermail/gnucash-devel/2019-May/043890.html gnucash-devel/2019-May].
;In '''XML''' it is more complex:
+
 
:;Glade: <syntaxhighlight lang="xml">
+
Standard '''icons''' are now specified in the XDG [https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html Icon Naming Specification]. This will allow each theme to use its own set.
<tag>Prefix "Quotation" Suffix.</tag>
+
 
</syntaxhighlight>
+
== Toolbars ==
:;DocBook: For attributes: <syntaxhighlight lang="xml">
+
Keep often used actions like <tt>Report options</tt> at the beginning of the list.
<sometag someattribute="value">Text</sometag>
 
</syntaxhighlight>
 
::In text: <syntaxhighlight lang="xml">
 
<p>Prefix <quote>Quotation</quote> Suffix.</p>
 
</syntaxhighlight>
 
::;Note: Depending on the semantic context there are more appropriate markups like <citation>, <guilabel>, <keycap>, ...
 
;HTML has several, depending on the context: <syntaxhighlight lang="html">
 
<p>Inline: normal <q>Quotation</q>, <code>Computer code</code> and <kbd>Keyboard input</kbd>. <em>Emphasis</em> and <strong>Strong</strong> should be preferred over <i>idiomatic</i> and <b>Bold</b>.</p>
 
<blockquote>A text
 
over several lines
 
</blockquote>
 
</syntaxhighlight>
 
''Translation teams'' are free to choose their locale common symbols as shown in [https://en.wikipedia.org/wiki/Quotation_mark Quotation mark].
 
:;Tip: Best practice is to note the convention in a comment in the header of the .po file.
 
  
= Mnemonics and Accelerators =
+
== Menus ==
 +
Menu elements should have a
 +
* [[#Mnemonics|mnemonic]] in their label and they should have a
 +
* [[#Tooltips_and_Descriptions_of_Preferences|tooltip]].
 +
;Ellipses: If a label ''specifies an action'', but further user interaction is required before, the label should have a trailing horizontal ellipse <tt>…</tt> (<code>altGr</code>+<code>.</code>), but not for dialogs like <tt>Properties</tt>, <tt>Preferences</tt>… See details at the bottom of https://developer.gnome.org/hig/stable/writing-style.html
  
 +
== Mnemonics and Accelerators ==
 
Gtk+ provides two means of creating "hot-keys" for keyboard operation of menu items and controls: [https://developer.gnome.org/gtk3/unstable/gtk3-Keyboard-Accelerators.html Accelerators] and special labels called '''mnemonics'''.
 
Gtk+ provides two means of creating "hot-keys" for keyboard operation of menu items and controls: [https://developer.gnome.org/gtk3/unstable/gtk3-Keyboard-Accelerators.html Accelerators] and special labels called '''mnemonics'''.
  
== Accelerators ==
+
=== Accelerators ===
 
Accelerators are normally assigned only to menu items, but they can be assigned to any control using a [https://developer.gnome.org/gtk3/unstable/GtkAccelLabel.html GtkAccelLabel]. ''"Can" does '''not''' mean "should"!'' Pressing the character together with the configured modifiers calls whatever function is linked to the control. Accelerators can be over-ridden by users using [https://developer.gnome.org/gtk3/unstable/gtk3-Accelerator-Maps.html an accelerator map]. Accelerators can be set in GtkBuilder/Glade files using the <code>accelerator</code> element.
 
Accelerators are normally assigned only to menu items, but they can be assigned to any control using a [https://developer.gnome.org/gtk3/unstable/GtkAccelLabel.html GtkAccelLabel]. ''"Can" does '''not''' mean "should"!'' Pressing the character together with the configured modifiers calls whatever function is linked to the control. Accelerators can be over-ridden by users using [https://developer.gnome.org/gtk3/unstable/gtk3-Accelerator-Maps.html an accelerator map]. Accelerators can be set in GtkBuilder/Glade files using the <code>accelerator</code> element.
  
 
;macOS Note: In most cases macOS prefers the &lt;command&gt; key to the &lt;control&gt; key as a modifier. Gtk provides a macro <code>GDK_MODIFIER_INTENT_PRIMARY_ACCELERATOR</code> that selects the correct modifier depending on OS. It should be used in most cases rather than <code>GDK_CONTROL_MASK</code>. As noted below under [[#Mnemonics|Mnemonics]] macOS uses the &lt;alt&gt; modifier key to extend the keyboard, so it should be used only with another not-&lt;shift&gt; modifier key in accelerators. Note that on macOS GDK_MOD2_MASK is the &lt;command&gt; key while on X11 it's &lt;numlock&gt; so either one must conditionally set accelerator modifiers (not possible in Glade), rely on an accelerator map to get a useable accelerator set, or restrict the modifiers to &lt;control&gt;&lt;alt&gt; and <code>GDK_MODIFIER_INTENT_PRIMARY_ACCELERATOR</code>. Unfortunately [https://glade.gnome.org/ Glade] does not support GdkModifierIntent and Gtk+ has supported it in GtkBuilder files only since 3.20 so it can be used only in accelerators defined in code.
 
;macOS Note: In most cases macOS prefers the &lt;command&gt; key to the &lt;control&gt; key as a modifier. Gtk provides a macro <code>GDK_MODIFIER_INTENT_PRIMARY_ACCELERATOR</code> that selects the correct modifier depending on OS. It should be used in most cases rather than <code>GDK_CONTROL_MASK</code>. As noted below under [[#Mnemonics|Mnemonics]] macOS uses the &lt;alt&gt; modifier key to extend the keyboard, so it should be used only with another not-&lt;shift&gt; modifier key in accelerators. Note that on macOS GDK_MOD2_MASK is the &lt;command&gt; key while on X11 it's &lt;numlock&gt; so either one must conditionally set accelerator modifiers (not possible in Glade), rely on an accelerator map to get a useable accelerator set, or restrict the modifiers to &lt;control&gt;&lt;alt&gt; and <code>GDK_MODIFIER_INTENT_PRIMARY_ACCELERATOR</code>. Unfortunately [https://glade.gnome.org/ Glade] does not support GdkModifierIntent and Gtk+ has supported it in GtkBuilder files only since 3.20 so it can be used only in accelerators defined in code.
  
 
+
===== GtkShortcuts =====
==== GtkShortcuts ====
 
 
The <code>GtkShortcutsWindow</code> is a convenient way to display all of GnuCash's accelerators to the user. Unfortunately it wasn't introduced until Gtk+-3.20.0 and we want to support
 
The <code>GtkShortcutsWindow</code> is a convenient way to display all of GnuCash's accelerators to the user. Unfortunately it wasn't introduced until Gtk+-3.20.0 and we want to support
 
:Gtk+-3.10 for GnuCash 3.x and
 
:Gtk+-3.10 for GnuCash 3.x and
 
:Gtk+-3.18 for GnuCash 4.x, so don't implement it now.
 
:Gtk+-3.18 for GnuCash 4.x, so don't implement it now.
  
== Mnemonics ==
+
=== Mnemonics ===
 
 
 
Mnemonics can be set on [https://developer.gnome.org/gtk3/unstable/GtkMenuItem.html#gtk-menu-item-new-with-mnemonic menu items] as well as [https://developer.gnome.org/gtk3/unstable/GtkButton.html#gtk-button-new-with-mnemonic buttons] or indeed any control by [https://developer.gnome.org/gtk3/unstable/GtkLabel.html#gtk-label-set-mnemonic-widget attaching] it to the [https://developer.gnome.org/gtk3/unstable/GtkLabel.html#gtk-label-new-with-mnemonic relevant label]. ''However'' one should be aware that menu-item mnemonics work quite differently: Mnemonics on controls operate like accelerators: Holding &lt;alt&gt; will reveal underlines on the mnemonic characters for the focused window or dialog and pressing an underlined character will operate the respective control. If the focused window has a menu bar associated with it the menu bar will be revealed if it's hidden and the mnemonics will be shown; pressing the mnemonic for a menu bar item will open that menu. At this point the &lt;alt&gt; can be released and the menu navigated by pressing the mnemonic keys alone. In addition to the linked functions, mnemonics can be set in GtkBuilder/Glade files with the <code>use_underline</code> and (on GtkLabels, not needed for GtkButtons) <code>mnemonic_widget</code> properties.
 
Mnemonics can be set on [https://developer.gnome.org/gtk3/unstable/GtkMenuItem.html#gtk-menu-item-new-with-mnemonic menu items] as well as [https://developer.gnome.org/gtk3/unstable/GtkButton.html#gtk-button-new-with-mnemonic buttons] or indeed any control by [https://developer.gnome.org/gtk3/unstable/GtkLabel.html#gtk-label-set-mnemonic-widget attaching] it to the [https://developer.gnome.org/gtk3/unstable/GtkLabel.html#gtk-label-new-with-mnemonic relevant label]. ''However'' one should be aware that menu-item mnemonics work quite differently: Mnemonics on controls operate like accelerators: Holding &lt;alt&gt; will reveal underlines on the mnemonic characters for the focused window or dialog and pressing an underlined character will operate the respective control. If the focused window has a menu bar associated with it the menu bar will be revealed if it's hidden and the mnemonics will be shown; pressing the mnemonic for a menu bar item will open that menu. At this point the &lt;alt&gt; can be released and the menu navigated by pressing the mnemonic keys alone. In addition to the linked functions, mnemonics can be set in GtkBuilder/Glade files with the <code>use_underline</code> and (on GtkLabels, not needed for GtkButtons) <code>mnemonic_widget</code> properties.
  
Line 54: Line 44:
 
Note that when one creates a mnemonic with an underscore the underscore becomes part of the label string that is a msgid for translation, so the same label with different mnemonics will result in multiple strings for translation. This is a good thing because it allows translators to select appropriate mnemonics for their languages.
 
Note that when one creates a mnemonic with an underscore the underscore becomes part of the label string that is a msgid for translation, so the same label with different mnemonics will result in multiple strings for translation. This is a good thing because it allows translators to select appropriate mnemonics for their languages.
  
= Menus =
+
= Textual content =
 
 
Menu elements should have a
 
* [[#Mnemonics|mnemonic]] in their label and they should have a
 
* [[#Tooltips_and_Descriptions_of_Preferences|tooltip]].
 
;Ellipses: If a label ''specifies an action'', but further user interaction is required before, the label should have a trailing horizontal ellipse <tt>…</tt> (<code>altGr</code>+<code>.</code>), but not for dialogs like <tt>Properties</tt>, <tt>Preferences</tt>… See details at the bottom of https://developer.gnome.org/hig/stable/writing-style.html
 
 
 
 
== Menu Entry Descriptions ==
 
== Menu Entry Descriptions ==
 
Sometimes you need to describe menu entries in other texts like tool tips, tip of the day, ...
 
Sometimes you need to describe menu entries in other texts like tool tips, tip of the day, ...
Line 70: Line 54:
 
:;conversion: "commodity -> currency" or "number to string".
 
:;conversion: "commodity -> currency" or "number to string".
  
= Toolbars =
+
== Quoting in Strings ==
Keep often used actions like <tt>Report options</tt> at the beginning of the list.
+
To get a unique appearance, the current team prefers ASCII double quotes <code>"</code> over single quotes <code>'</code> or non-ASCII characters.
 
+
;So ''developers'' should use in '''C''' etc.: <syntaxhighlight lang="C">
= Buttons and Icons =
+
Msg= "Prefix \"Quotation\" Suffix."
For [https://docs.google.com/document/d/1KCVPoYQBqMbDP11tHPpjW6uaEHrvLUmcDPqKAppCY8o/pub GTK+ 3.10 Stock Items Deprecation] announced on [https://mail.gnome.org/archives/gtk-devel-list/2013-July/msg00000.html gtk-devel-list/2013-July] and the
+
</syntaxhighlight>
[https://docs.google.com/spreadsheets/d/1HavJQRPpMuq-N0GoN1wJR-9KEGXpKy3-NEPpZZkUGJY/pub?output=html Replacement Table] watch the current discussion starting with [https://lists.gnucash.org/pipermail/gnucash-devel/2019-May/043890.html gnucash-devel/2019-May].
+
;In '''XML''' it is more complex:
 
+
:;Glade: <syntaxhighlight lang="xml">
Standard '''icons''' are now specified in the XDG [https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html Icon Naming Specification]. This will allow each theme to use its own set.
+
<tag>Prefix "Quotation" Suffix.</tag>
 
+
</syntaxhighlight>
= Tooltips and Descriptions of Preferences =
+
:;DocBook: For attributes: <syntaxhighlight lang="xml">
 +
<sometag someattribute="value">Text</sometag>
 +
</syntaxhighlight>
 +
::In text: <syntaxhighlight lang="xml">
 +
<p>Prefix <quote>Quotation</quote> Suffix.</p>
 +
</syntaxhighlight>
 +
::;Note: Depending on the semantic context there are more appropriate markups like <citation>, <guilabel>, <keycap>, ...
 +
;HTML has several, depending on the context: <syntaxhighlight lang="html">
 +
<p>Inline: normal <q>Quotation</q>, <code>Computer code</code> and <kbd>Keyboard input</kbd>. <em>Emphasis</em> and <strong>Strong</strong> should be preferred over <i>idiomatic</i> and <b>Bold</b>.</p>
 +
<blockquote>A text
 +
over several lines
 +
</blockquote>
 +
</syntaxhighlight>
 +
''Translation teams'' are free to choose their locale common symbols as shown in [https://en.wikipedia.org/wiki/Quotation_mark Quotation mark].
 +
:;Tip: Best practice is to note the convention in a comment in the header of the .po file.
  
 +
== Tooltips and Descriptions of Preferences ==
 
Tooltips should contain at least one full sentence.
 
Tooltips should contain at least one full sentence.
 
+
;Purpose:
 +
:#Describe the impact of the GUI element,
 +
:#give the user a clue about the "normal" state.
 
The separator between menu elements is "->" like "Menu->SubMenu->MenuItem".
 
The separator between menu elements is "->" like "Menu->SubMenu->MenuItem".
  
Tooltips of ''preferences'' have usually 3 occurences:
+
;Tooltips of ''preferences'':
* glade: Edit->Preferences->... <code><property name="tooltip_text" translatable="yes">your text</property></code>
+
: have usually 3 occurences:
* gschema (xml): <code><description>your text</description></code> (displayed in RegEdit, dconf-editor, ...)
+
# glade: Edit->Preferences->... <syntaxhighlight lang="xml"><property name="tooltip_text" translatable="yes">your text</property></syntaxhighlight>
* gnucash-help/custom-gnucash... (docbook xml): <syntaxhighlight lang="xml">  <listitem>
+
# gschema (xml), displayed in RegEdit, dconf-editor, ...: <syntaxhighlight lang="xml"><description>your text</description></syntaxhighlight>
     <para><guilabel>Include grand total:</guilabel> If checked, show in the <emphasis>Summarybar</emphasis> a grand total of all accounts converted to the default currency.</para>
+
# gnucash-help/custom-gnucash... (docbook xml): <syntaxhighlight lang="xml">  <listitem>
 +
     <para><guilabel>Include grand total</guilabel>: If checked, show in the <emphasis>Summarybar</emphasis> a grand total of all accounts converted to the default currency.</para>
 
   </listitem></syntaxhighlight>
 
   </listitem></syntaxhighlight>
  
Use for all the same text to keep it simple for translators. They should not feel like in the [https://en.wikipedia.org/wiki/Colossal_Cave_Adventure colossal cave adventure]:
+
Use for all the same text to keep it simple for translators. They should not feel like in the [https://en.wikipedia.org/wiki/Colossal_Cave_Adventure colossal cave adventure]: <syntaxhighlight lang="console">
You are in a maze of twisty little passages, all alike.
+
You are in a maze of twisty little passages, all alike.
You are in a maze of twisty little passages, all different.  
+
You are in a maze of twisty little passages, all different.  
You are in a little maze of twisty passages, all different.
+
You are in a little maze of twisty passages, all different.
You are in a little maze of twisting passages, all different.
+
You are in a little maze of twisting passages, all different.
:
+
:
 +
</syntaxhighlight>
  
 
=Reference=
 
=Reference=

Revision as of 20:26, 31 October 2020

This page collects rules for the GUI. You should mind them while coding or preparing translation (I18N).

GUI Resolution

The maximum size of all GUI elements restricts users to have at least the same resolution on their device to run GnuCash flawless. Bug 797857 - Edit->Preferences: Help/Close buttons unreachable remembered us about this restriction. For

GnuCash 3 and up
the limit is 1024x768. In the
GnuCash 2.x series
it was 800x600.

GUI Elements

Buttons and Icons

For GTK+ 3.10 Stock Items Deprecation announced on gtk-devel-list/2013-July and the Replacement Table watch the current discussion starting with gnucash-devel/2019-May.

Standard icons are now specified in the XDG Icon Naming Specification. This will allow each theme to use its own set.

Toolbars

Keep often used actions like Report options at the beginning of the list.

Menus

Menu elements should have a

Ellipses
If a label specifies an action, but further user interaction is required before, the label should have a trailing horizontal ellipse (altGr+.), but not for dialogs like Properties, Preferences… See details at the bottom of https://developer.gnome.org/hig/stable/writing-style.html

Mnemonics and Accelerators

Gtk+ provides two means of creating "hot-keys" for keyboard operation of menu items and controls: Accelerators and special labels called mnemonics.

Accelerators

Accelerators are normally assigned only to menu items, but they can be assigned to any control using a GtkAccelLabel. "Can" does not mean "should"! Pressing the character together with the configured modifiers calls whatever function is linked to the control. Accelerators can be over-ridden by users using an accelerator map. Accelerators can be set in GtkBuilder/Glade files using the accelerator element.

macOS Note
In most cases macOS prefers the <command> key to the <control> key as a modifier. Gtk provides a macro GDK_MODIFIER_INTENT_PRIMARY_ACCELERATOR that selects the correct modifier depending on OS. It should be used in most cases rather than GDK_CONTROL_MASK. As noted below under Mnemonics macOS uses the <alt> modifier key to extend the keyboard, so it should be used only with another not-<shift> modifier key in accelerators. Note that on macOS GDK_MOD2_MASK is the <command> key while on X11 it's <numlock> so either one must conditionally set accelerator modifiers (not possible in Glade), rely on an accelerator map to get a useable accelerator set, or restrict the modifiers to <control><alt> and GDK_MODIFIER_INTENT_PRIMARY_ACCELERATOR. Unfortunately Glade does not support GdkModifierIntent and Gtk+ has supported it in GtkBuilder files only since 3.20 so it can be used only in accelerators defined in code.
GtkShortcuts

The GtkShortcutsWindow is a convenient way to display all of GnuCash's accelerators to the user. Unfortunately it wasn't introduced until Gtk+-3.20.0 and we want to support

Gtk+-3.10 for GnuCash 3.x and
Gtk+-3.18 for GnuCash 4.x, so don't implement it now.

Mnemonics

Mnemonics can be set on menu items as well as buttons or indeed any control by attaching it to the relevant label. However one should be aware that menu-item mnemonics work quite differently: Mnemonics on controls operate like accelerators: Holding <alt> will reveal underlines on the mnemonic characters for the focused window or dialog and pressing an underlined character will operate the respective control. If the focused window has a menu bar associated with it the menu bar will be revealed if it's hidden and the mnemonics will be shown; pressing the mnemonic for a menu bar item will open that menu. At this point the <alt> can be released and the menu navigated by pressing the mnemonic keys alone. In addition to the linked functions, mnemonics can be set in GtkBuilder/Glade files with the use_underline and (on GtkLabels, not needed for GtkButtons) mnemonic_widget properties.

Mnemonics have two problems on Macs
First, they don't work on the menu. Keyboard menu navigation is accomplished by pressing <ctrl>F2 (don't forget to also press <fn> on keyboards that use one unless you've flipped the <fn> key behavior in Keyboard Preferences) to activate the menubar and then navigating with the cursor keys. Second, macOS used the <alt> key to extend the keyboard; for example on a US keyboard one would type <alt>e e to get é or <alt>o to get ø. Setting a mnemonic will grab the event before the text control gets it and prevent that character from being typed.

Note that when one creates a mnemonic with an underscore the underscore becomes part of the label string that is a msgid for translation, so the same label with different mnemonics will result in multiple strings for translation. This is a good thing because it allows translators to select appropriate mnemonics for their languages.

Textual content

Menu Entry Descriptions

Sometimes you need to describe menu entries in other texts like tool tips, tip of the day, ...

In that case use "->" without spaces as separator of the levels.

Example
"File->Open…"

Avoid "->" for other contexts like

range
"1 … 10, A … Z" or
conversion
"commodity -> currency" or "number to string".

Quoting in Strings

To get a unique appearance, the current team prefers ASCII double quotes " over single quotes ' or non-ASCII characters.

So developers should use in C etc.
Msg= "Prefix \"Quotation\" Suffix."
In XML it is more complex
Glade
<tag>Prefix "Quotation" Suffix.</tag>
DocBook
For attributes:
<sometag someattribute="value">Text</sometag>
In text:
<p>Prefix <quote>Quotation</quote> Suffix.</p>
Note
Depending on the semantic context there are more appropriate markups like <citation>, <guilabel>, <keycap>, ...
HTML has several, depending on the context
<p>Inline: normal <q>Quotation</q>, <code>Computer code</code> and <kbd>Keyboard input</kbd>. <em>Emphasis</em> and <strong>Strong</strong> should be preferred over <i>idiomatic</i> and <b>Bold</b>.</p>
<blockquote>A text 
over several lines
</blockquote>

Translation teams are free to choose their locale common symbols as shown in Quotation mark.

Tip
Best practice is to note the convention in a comment in the header of the .po file.

Tooltips and Descriptions of Preferences

Tooltips should contain at least one full sentence.

Purpose
  1. Describe the impact of the GUI element,
  2. give the user a clue about the "normal" state.

The separator between menu elements is "->" like "Menu->SubMenu->MenuItem".

Tooltips of preferences
have usually 3 occurences:
  1. glade: Edit->Preferences->...
    <property name="tooltip_text" translatable="yes">your text</property>
    
  2. gschema (xml), displayed in RegEdit, dconf-editor, ...:
    <description>your text</description>
    
  3. gnucash-help/custom-gnucash... (docbook xml):
      <listitem>
        <para><guilabel>Include grand total</guilabel>: If checked, show in the <emphasis>Summarybar</emphasis> a grand total of all accounts converted to the default currency.</para>
      </listitem>
    
Use for all the same text to keep it simple for translators. They should not feel like in the colossal cave adventure:
You are in a maze of twisty little passages, all alike.
You are in a maze of twisty little passages, all different. 
You are in a little maze of twisty passages, all different.
You are in a little maze of twisting passages, all different.
:

Reference

Human Interface Guidelines

As long as we use GTK, GNOMEs HIG is the primary source. But sometimes the comparision with other HIGs, can be useful:

macOS Human Interface Guidelines
Win32 apps Guidelines
KDE Human Interface Guidelines