After several years of tweaking I found I was getting lost as to 'what does what'. Hence this file. I have tried to relate actions and relevant paths. It is far from complete but hopefully it helps debug or open the way to any modding you might consider.

Menu tabs:
the relevant tab-page is loaded through plugin.php – // MENU tab links ~#105

LISTS: loads galListView.php
toggle Default Thumbsize: click #cropChange > $('body').on('click', '#cropChange'
    saves in plugin.php > if (isset($_POST['saveThumbSize']))
'edit' routes via plugin.php > viewAllImages.php

UPLOAD:
toggle 'how to' > viewAllImages.php > on('click', '#hideDataDetail'
    $.get to php/ajaxDataDo.php?toggleHowTo > writes to php/howToDetail.txt
uploader.php > plugin.php > if ( isset($_FILES['fileToUpload']['error']) [builds empty tag file]



NEW:
create a new gallery
Note the shared interface use of new/edit > if (isset($_GET['edit'])
Data is processed in plugin.php > if (isset($_POST['saveMG']))
adding image > imagebrowser.php

DATA:
view album contents and details of images
toggle 'how to' > see 'UPLOAD' above
click album bar > $.get to php/ajaxDataDo.php?getAlbData > item 1
    if (isset($_GET['getAlbData'], $_GET['album']))
    this writes image paths
image use: php/ajaxDataDo.php?getUseData > item 2
    if (isset($_GET['getUseData'], $_GET['fileImage']))
    data is copied to clipboard
delete: plugin.php > if (isset($_GET['delImg']))


TAGS:
Content for all three buttons is written in tags.php 
    <div id="addNew" ~ #49
    <div id="imageTagging" ~ #111
    <div id="tagSorting" ~ #157
➕ Tags ➖ > uses bl-content/imageManager/imageManagerList/tagList.txt
    'Remove Tags' > plugin.php > if (isset($_POST['removeTags'])) { ... }
open album: in tags.php > $('body').on('click', '[id^="zzz"]', function(e) {
    actions... $.get('<?= HTML_PATH_ROOT ?>bl-plugins/imageManager/php/ajaxTagDo.php?getTagData
    & ajaxTagDo.php adds data to <div id="xxx'.$folder.'" (in tags.php)
    there are two forms: id="formA" runs 'save tags' + id="formB" runs 'SAVE'
    formA saves in plugin.php > if (isset($_POST['saveTagEdit'])) { ... }
    formB saves in plugin.php > if (isset($_POST['addSelected'])) { ... }