With the documentation site MODX Extras | MODX Documentation, in the sidebar scrolling menu, have you considered adding some JavaScript to center the side menu on the active element when changing pages?
Something like the following perhaps.
// Center Side Menu on Active Element
window.onload = function() {
var container = document.getElementByID('nav');
var activeElement = container.querySelector('..c-nav__item--activepage');
if (activeElement) {
activeElement.scrollIntoView({ behavior: 'auto', block: 'center' });
}
};
Second, perhaps also a quick-search box at the top to filter all the menu items. The following might work, or should be close.
// Search and Filter the Side Menu
<input type="search" id="searchbox" onkeyup="searchNav()" placeholder="Menu Search" />
document.getElementById('searchbox').addEventListener('input', searchNav);
function searchNav() {
// Declare variables
var input, filter, ul, li, a, i, txtValue;
input = document.getElementById('searchbox');
filter = input.value.toUpperCase();
ul = document.getElementById("nav");
li = ul.getElementsByTagName('li');
// Loop through all list items, and hide those who don't match the search query
for (i = 0; i < li.length; i++) {
a = li[i].getElementsByTagName("a")[0];
txtValue = a.textContent || a.innerText;
if (txtValue.toUpperCase().indexOf(filter) > -1) {
li[i].style.display = "";
} else {
li[i].style.display = "none";
}
}
}