How to use begin with selector in Less - css-selectors

Question

I'm going to create a less code that will give different background-color to element depending on it's class. This will be for list of attachments, so class name is based on attachment extension.
I do support some typical extensions:
.label{
&.label-pdf{
background-color: #c70000;
}
&.label-doc, &.label-docx, &.label-odt{
background-color: #157efb;
}
&.label-xls, &.label-xlsx, &.label-calc{
background-color: #069e00;
}
&.label-ppt, &.label-pptx, &.label-odp{
background-color: #9e3c15;
}
&.label-jpg, &.label-png, &.label-gif, &.label-png, &.label-ttf{
background-color: #95009e;
}
}
but the problem is with some unusual extensions, or even files like: jpg, jpeg, doc, docx, this is why I would like to use expression from CSS. In pure CSS I could use:
.label.[class^="label-"]{
background-color: rgba(0,37,100,0.4);
}
And put this code at the beginning so other classes could override this one.
But unfortunately this sign ^ (I suppose) is breaking my Less compilation. I have been trying to do something like this:
~".label.[class^='label-']{
background-color: rgba(0,37,100,0.4);
}"
AND
.label{
&.~"[class^='label-']"{
background-color: rgba(0,37,100,0.4);
}
}
But still not working. So is it possible to use this selector?

Answer 1

It is not working because your syntax seems to be wrong and not because of any issues with Less.
The below code is invalid because of the . present between the label and the class^="label-"]. Attribute selectors do not require a . before them. It is necessary only for class selectors.
.label.[class^="label-"]{
background-color: rgba(0,37,100,0.4);
}
The correct version would be the following:
.label[class^="label-"]{
background-color: rgba(0,37,100,0.4);
}
and so in Less terms, if you want nesting, it would be as follows:
.label{
&[class^='label-']{
background-color: rgba(0,37,100,0.4);
}
}
.label.[class^="label-"] { /* this won't work */
background-color: rgba(0, 37, 100, 0.4);
}
.label[class^="label-"] { /* this will */
color: green;
}
<label class='label-a label'>Label A</label>
<label class='label-b label'>Label B</label>
Another thing to note is that the ^= is a starts with selector and so when your element has more than one class, the class that resembles label- should be the first class in the list and not the label. If we make the label as the first class then (like seen in below snippet) it won't work because then the class doesn't start with label-.
If the first class in the list is indeed label then you should consider using the *= (contains) selector. But be careful when using the contains selector because it will sometimes select unintended elements like those with class label-not, not-label etc.
.label.[class^="label-"] { /* this won't work */
background-color: rgba(0, 37, 100, 0.4);
}
.label[class^="label-"] { /* this won't too */
color: green;
}
.label[class*="label-"] { /* this will */
border: 1px solid green;
}
<label class='label label-a'>Label A</label>
<label class='label label-b'>Label B</label>

Answer 2

I have same problem. I use this in less file.
[class^="customForm-"] { ... }
But for my HTML it does not works.
<div class="form form-01 customForm-radioList">...</div>
The problem is in tha fact that string "form form-01 customForm-radioList" does not starts with "customForm-" it starts with "form".
Solution
Use contains selector W3 school.
[class*="customForm-"] { ... }